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Every Datapoint a Person

Description of a Slave Ship

Before there are data, there are people. People who offer up their lives as data — or whose lives become data without consent.

It was a long and circuitous—and often painful—path that led Olaudah Equiano, the famed author and abolitionist, to London in January 1777. According to his autobiography, The Interesting Narrative of the Life of Olaudah Equiano, or Gustavus Vassa, the African (1789), Equiano was born in the Igbo area of the Kingdom of Benin, in what is now southeastern Nigeria. Kidnapped from his birthplace at the age of 11 and carried to the Atlantic coast, Equiano was then forced aboard a slave ship. There he encountered "a multitude of black people of every description chained together," the captives packed in quarters "so crowded that each had scarcely room to turn himself." Equiano was taken to Barbados and then to Virginia, where he was sold. He would remain enslaved for almost twenty years.

By the time that Equiano settled in London, he had been free for over a decade; in 1766, Equiano had purchased himself, and therefore his freedom, with earnings from his personal trading business. But his experience of enslavement was never far from his mind. And so in the late 1780s, as the British antislavery movement began to coalesce, Equiano became increasingly involved in its activities. Through this abolitionist work, he became acquainted with Thomas Clarkson, a leading white abolitionist and key member of the London Committee of the Society for Effecting the Abolition of the Slave Trade (SEASE). So when, in early 1789, Clarkson received a copy of a diagram created by the Plymouth Committee of SEASE entitled, "Plan of an African Ship's Lower Deck with Negroes in the Proportion of Only One to a Ton," he knew exactly who he should ask to confirm the truth of what he saw.

An aerial view of a ship's hold, filled with four rows of small human figures, packed shoulder to shoulder.

The diagram that Clarkson showed to Equiano depicted the configuration of captive bodies in the hold of a slave ship—a "scene of horror almost inconceivable," as Equiano, in his autobiography, described his own first view into the hold, and that his fellow Black British antislavery activist Quobna Ottobah Cugoano, in his own treatise, Thoughts and Sentiments on the Evil and Wicked Traffic of the Slavery and Commerce of the Human Species (1787), recalled as such a trauma that he chose not to describe it at all. But in the diagram that Clarkson received from the Plymouth Committee, and that he shared with Equiano, Clarkson believed he'd found the key to conveying the depth of this inhumanity to his white compatriots. The diagram, which he would go on to revise and extend, and publish in March of that year as "Description of a Slave Ship," would create an "instantaneous impression of horror upon all who saw it," Clarkson later recalled, and compel them to join the abolitionist cause.

The "instantaneous impression of horror" that Clarkson hoped his diagram would prompt was, like all carefully-engineered viewing experiences, the result of countless hours of research and design. Given the actual words that Clarkson employed—and in particular, the "instantaneous impression"—it also safe to say that the diagram represented the culmination of over two centuries of thinking about the value of empirical evidence and the impact of giving it visual form. Indeed, the idea that evidence could be visualized as data, perceived by the eyes, and then processed into knowledge by the mind, coalesced from the contributions of empiricism in both theory and practice, as well as an increasingly wide array of examples of how numbers and the relationships among them could be abstracted into images that the eye could perceive.

This intellectual genealogy is, as readers might recall, the first of the two stories of data visualization presented in this project's introduction. But in the "horror" that Clarkson engineered his chart to produce, the second story of data visualization—the one having to do with the uneasy alliance between slavery and data—also snaps into view. "Description of a Slave Ship" requires that we consider these two stories together, and in so doing, demonstrates the importance of this braided narrative for the history of the field. This expanded account underscores the tremendous power of data visualization to distill complex information such that insight can easily and efficiently emerge, while at the same time reminding us—both those who design visualizations and those who perceive them—how the abstraction that is required to efficiently generate insight always comes at the expense of additional detail—detail that data alone cannot convey.

Setting "Description of a Slave Ship" at the center of the story we tell about the emergence of modern data visualization also reminds us that the context of any particular visualization always matters—and that context carries with it both social and political force. More basically, and more profoundly, Clarkson's "Description" reminds us that before there are data there are people—people who offer up their lives to be counted as data, or have their lives counted without their consent. The act of transforming people into data, and of putting that data on display, are both tremendous acts of power. And that power is not guaranteed to always be a benevolent force. Centering "Description of a Slave Ship" in the story we tell about the emergence of data visualization is thus long overdue, for it requires that we recognize the responsibility that comes with this power—the power of visualizing data—which frames what is possible for the viewer to know.

The original engraving that Clarkson showed to Equiano, and that provided him with the visual model for his own, is attributed to the Plymouth Committee as a collective. But it is generally believed that the image was designed by a single man: William Elford, the Committee's chairman and a veritable polymath. A banker by trade, Elford was also an acclaimed painter whose landscapes had shown at the Royal Academy of Arts, as well as an amateur scientist whose experiments had earned him membership in the Royal Society, the highest scientific honor of the time. (Locke, Boyle, Plot, and others mentioned in the Introduction were also members).

Supplementing this range of skills was domain expertise: Elford had family ties to the Royal Navy, and as a result, had early access to a report being prepared by one of its naval captains. Earlier in the year, a group within the British Parliament had tasked the captain, Parrey, with investigating the ships docked in Liverpool that were involved in the transatlantic slave trade. This investigation took both quantitative and qualitative form; in addition to taking precise measurements of the ships and scrutinizing muster logs—lists of crew members aboard any particular ship—Parrey also interviewed the captains and sailors of the ships themselves, learning otherwise undisclosed information about the perils faced by both captives and crew.

The art historian Cheryl Finley, whose book Committed to Memory: The Art of the Slave Ship Icon explores the origins and evolving significance of the "Description" in extensive detail, speculates that among the "most useful" artifacts from Parrey's report were the hand-drawn diagrams of the ships created by the captains themselves. Intended as "a type of visual shorthand apparently used to increase the efficiency of packing ships," for abolitionist viewers, these sketches likely became a graphic call to arms. Elford, for one, saw a direct visual depiction of the dehumanization that was required in order to reduce human lives into commodity goods on the part of slavery's profiteers.

Readers have already been informed that the default settings for this chapter hide the visual details of the "Description," and the other sensitive images discussed here, until they are sufficiently prepared for what they might see. We made this choice because of the range of harms that can be brought about by engaging with the archive of slavery without warning, context, or consent. These harms may be retrospective, the result of "the uncertain line between witness and spectator" that scholars of slavery often walk, as literary scholar Saidiya Hartman has influentially written. They may also be expressed in the form of the desensitization brought about by evermore depictions of the "routinized violence of slavery," Hartman further explains. For viewers whose own ancestors were enslaved, such depictions can also exacerbate existing intergenerational trauma, as historian Jennifer Morgan describes. Those who choose to view Elford's version of the diagram may do so now by clicking the button at the bottom right. Or you may choose to continue to only read about the images of slavery included here.

Indeed, Elford's diagram—the one that Equiano saw—is as viscerally affecting as it is visually impossible. Viewers see the ship from above, as if they are gods in the heavens. (We will return to what is, in fact, a "god trick" down below). The top deck of the ship has been removed, so that the viewer can see directly into the hold.

120 male bodies in4 rows of 30.72 boybodies inin 6 rowsof 12.84 female bodies in4 rows of 21.30 girlbodies in3 rowsof 10.

The hold is divided into six distinct areas.

The largest area, in the bow of the ship, and which occupies the entire right half of the diagram, is labeled the "Mens room," and depicts 120 male bodies in four rows of thirty.

In the middle is a narrow column labeled "Boys room" and depicts shorter male figures in six rows of twelve.

To its left is the larger "Womens room," depicting figures the same size as the adult men, but with breasts. They are depicted in four rows of twenty-one, representing 84 women total.

At the stern is the "Girls Room," the figures shorter and squatter than the boys, arranged in three rows of ten.

These "scaled inequalities," as Black feminist theorist Hortense Spillers characterizes the figures, literalize the process of "dehumanizing, ungendering, and defacing" that the Middle Passage brought about.

Certain visual features help the plan achieve its impact. Most immediate is how the 297 figures, what Marcus Wood describes as a "mass of black human flesh," are set against the clean lines that indicate the bounds of the ship. The labels of each area, engraved in neat script, underscore the reduction in complexity that is intended by the diagram. Wood describes the design of the Plan in terms of an "awful rigor," underscoring how the "formality" of the figures "appears to deny [their] flesh and blood presence." But for Elford, this abstraction was perhaps part of the point.

It is unknown as to whether Elford was familiar with an earlier, more literal depiction of a slave ship, the Marie Séraphique, which dates to around 1770. This image, "Plan, Profile, et Distribution du Navire La Marie Seraphique," commissioned by the ship's owner to commemorate the "successful" return of its first slaving voyage, presents a view of the hold—and the captives within it—as one of four cross-sections of each of the ship . The image also includes a watercolor of the ship arriving into Loango , in what is now Republic of Congo, where the 312 captives were first purchased by the French captain,as well as data tables that sort them by gender and age , as well as by whether or not they survived.

This "Plan" is shocking in its attempt at realism. Unlike the "cartoon figures" in Elford's diagram, as Spillers also describes them, the captives depicted here are each individually drawn. They are shown lying on their sides. Most are naked, but several are clothed . The men are shackled —some with their arms and legs shackled to each other; others shackled to two-by-two. One woman nurses a child.

Regardless of whether Elford saw this particular chart, he clearly considered what he would give visual form and what he would not. As evidence, consider how, in contrast to the diagram of the Marie Séraphique, the two areas of Elford's diagram labeled "store room" are left blank, even as they were presumably packed with samebarrels and other dry goods that were required to sustain the captives and crew. Here, the white space of the store rooms instead emphasizes the diagram's rhetorical point: that the slave trade primarily entailed the packing of people as cargo aboard a ship.

At the same time, Elford could not but himself also participate in this process of dehumanization, however inadvertently. A large part of how the diagram achieves its visual impact is how its 297 human souls are drawn as nearly identical figures—what historian Marcus Wood, in reference to Spillers, describes as a "mass of black human flesh." The figures' collective rather than individual significance is further accentuated by their being set against the clean lines that indicate the bounds of the ship. The labels associated with each area, engraved in neat script, underscore this reduction in complexity—which is, of course, a reduction in humanity as well.

It is here that the significance of the diagram for the larger practice of data visualization begins to cohere: Elford's design achieves its success because of its strategic use of abstraction. It represents the captives as almost proto-Isotypes, rather than individual people each with unique bodily features and expressions pointing to inner lives. In so doing, Elford "induce[s] viewers to think about the substance of the data" of the slave trade, to employ Tufte's language, rather than about anything else. Yet Elford achieves this singular focus by stripping away the individual lives behind each datapoint. These lives are, paradoxically, the very same that he designed his charts in order to support.

Not all data visualizations take on this most odious episode in human history, of course. But this particular lesson about the chart's constitutive tension is one that can be more universally applied. The abstraction that is required to efficiently produce insight always—and necessarily—comes at the expense of the full complexity of the phenomenon that it represents. What should we do with this realization, either as viewer of data visualizations or as designers of them? The answer is not that we should reject visualization out of hand. Rather, it is that we must always consider what is lost in the process of visualizing data at the same time that we consider what is gained.

Elford's diagram also reminds us, with its subject most profound, that there are aspects of human experience that data visualization cannot and can never convey. No diagram can ever express the full extent of the brutality and degradation that was required to enforce the enslavement of otherwise equals. No diagram can ever fully communicate the "horror almost inconceivable," to return to Equiano's chilling words, to those who did not personally experience it; nor can any diagram appropriately convey the additional trauma that others, like Cugoano, chose to keep suppressed. As above, the lesson is not of the futility of visualizing data. It is, rather, one of hope: that with the image of the slave ship indelibly etched in our minds, we will keep the uses and limits of data visualization together in view. The power to produce an "instantaneous impression" in the eyes of viewers remains among the greatest strengths of data visualization. But as we consider this tremendous power, we must also—always—consider our responsibility for the insights that we design our visualizations in order to prompt, the knowledge they may lead to, and the detail and context—and in this case, the lives—that visualization alone cannot convey.

A page divided into three sections depicts the human captives and products for sale in a ship’s hold. The images are colored rather than monochromatic, like Elford’s graphic discussed earlier in the chapter.

An early engraving that makes use of the aerial view of the ship's hold, displaying its human captives alongside its goods for sale.An early engraving that makes use of the aerial view of the ship's hold, displaying its human captives alongside its goods for sale.Image courtesy of Wikimedia Commons.

As Elford was scrutinizing the Parrey report, William Clarkston was pursuing his own research into the pernicious nature of the slave trade. Like Parrey, Clarkston began by transforming the available records into data. He visited merchant halls in order to examine the muster rolls stored there, and used them to compute mortality rates among the sailors aboard the ships. (The dangers of the slave trade to the sailors, who were predominantly white, would become a highly persuasive piece of evidence in the argument for its abolition.) While examining the muster rolls, Clarkson also covertly transcribed 20,000 of the sailors' names. He then sought out individual sailors—primarily those who had been mistreated or maimed—whom he thought might be willing to speak about the conditions aboard the ships (both those that they personally experienced and those of the captives that they observed). These efforts at an early form of mixed-methods research underscore Clarkson how understood the value of empirical evidence—qualitative as well as quantitative—in advancing his abolitionist claims.

This view of the value of evidence of multiple forms, as well as the value of multiple forms of display, strongly influenced Clarkson's revisions to the original diagram. While Elford and the Plymouth Committee had first printed the diagram as a companion to a four-page abolitionist pamphlet, and later as a broadside version with the image at the top, it was Clarkson who insisted that the London Committee's version also include data tables. The tables included measurements of the ship, the Brooks, that had been used as a model for the diagram, and a conversion scale that indicated precisely how much square footage had been intended to be allocated to each captive on the chart. A second set of tables enabled a comparison between the number of captives who had actually been held on the original ship and the smaller number depicted in the diagram. This additional information was intended to "give a representation of the trade against which no complaint of exaggeration could be brought." It also underscores the fact that "Description of Slave Ship" was, like its predecessor, a data visualization. The "Description" has at times been dismissed from the visualization pantheon because of its political orientation, and because it is perceived to be an "infographic"—a direct representation of data—rather than an abstraction of more complex information. But "Description of a Slave Ship" in fact employs both of the grounding criteria of that era's definition of visual display: making "previously invisible phenomena subject to direct inspection," as Michael Friendly and Howard Wainer propose, and making those phenomena "palpable and concrete."

To wit: just as Clarkson's reintroduction of data to the chart underscored its basis in empirical evidence and buttressed its claims to the truth, so too did his visual modifications. More specifically, he shifted the view of the hold lower down the page, and added a series of cross-sections that showed additional views of the ship from the side. The inclusion of the cross sections drew from the conventions of naval architectural plans, which were by that time strongly established. This had the rhetorical effect of securing the chart's "graphic authority," as Marcus Wood describes it, in ways similar to how drawing new national borders on an existing map leveraged the power of its seemingly documentary form. Unlike a typical naval diagram—or, for that matter, a typical map—Clarkson's cross-sections also included people. These represented the captives themselves, whom Clarkson included as a way to show from multiple perspectives precisely how they were confined.

Part graphic and part text, this spread depicts and expounds upon the various sections of a slave ship. The top half of the page shows the images, while the bottom half contains small typescript explanations of the diagrams in the top half.
Part graphic and part text, this spread depicts and expounds upon the various sections of a slave ship. The top half of the page shows the images, while the bottom half contains small typescript explanations of the diagrams in the top half. On the right-hand side of the page, three different views of the length of the ship are printed in vertical succession: the first, labeled Fig. I, is a side-facing view of the outside of the ship, while the two underneath, labeled FIg. V and Fig. IV, respectively, are aerial views of a ship’s hold on the two levels below the deck. Each wall of the ship and its different rooms and levels is assigned a capital letter of the alphabet, so as to indicate consistency between the various perspective views of the ship. On the left-hand side of the page, four smaller images of stacked compartments and rooms in the ship are shown in more detail, labeled Fig III., Fig. II, Fig. VII, and Fig. VI, respectively. The top two figures on the left–figures III and II–show side views of the back of the ship (levels K, N, M, H, G, and O), while the bottom two figures–VII and VI–show aerial views beneath the deck. Keeping with the abstraction of the abovementioned Plan, the captured people on board are drawn with no remarkable individual features, merely shaded in black in a shape resembling the human body from the aerial views of the ship (shown in figures IV, V, VI, and VII). Moreover, the side views of the vessel–figures I, II, and III–abstract further from the human form by representing people by simple semicircles, which often overlap and lump together, to give the impression of heads in the hold of the ship.
A revised version of "Plan of an African Slave Ship" created by the London Committee of Society for Effecting the Abolition of the Slave Trade in England in 1789. This version expands upon the original diagram by including additional cross sections, as well as statistics and explanatory text. Image courtesy of the Beinecke Rare Book and Manuscript Library, Yale University.
Cross-sections of each deck.Side views.Small typescript explanations.Title: "Description of a Slave Ship".Data tables.Ship measurements.Tabulation of captives held on the ship.Comparison of actual captives and those pictured.

Clarkson created a series of cross-sections that showed each deck from above.

From the side—cross-sections that, like the Plymouth Committee's "Plan," included human figures intended to indicate how the captives were confined.

The result was a set of schematics that carried with them the connotations of accuracy and precision that were associated with the naval diagrams of the time, and yet also enlisted what Ian Baucom characterizes as a "sympathetic grammar" intended to draw those who viewed the chart to the antislavery cause.

Clarkson's revised chart, entitled "Description of a Slave Ship," was—like the original "Plan,"--accompanied by explanatory text.

In addition to the text, Clarkson also included a set of tables intended to reinforce the factual nature of the evidence visualized above.

The first table shows measurements of the actual ship, along with a scale that indicated how they corresponded to the image.

There was a small tablet that presented information about the number of captives that had actually been held on the ship.

The final table presented a comparison between the number of actual captives and those pictured on the diagram, making clear that while the image is informed by data, it is not a direct representation of those numbers and lives.

Here we might recall how Elford's diagram depicted the captives' bodies with minimal differentiation, which scholars have largely interpreted as reflecting "an abolitionist cultural agenda which dictated that slaves were to be visualized in a manner which emphasized their total passivity and prioritized their status as helpless victims." In Clarkson's version, however, the captives are shown wearing loincloths. The men are shackled together in pairs, by both their hands and by their feet. The women, on the other hand, remain unbound, and with their breasts exposed.

The combined effect was a diagram that engaged the viewer through two very different epistemological registers, both at the same time. First, as a representation of the data that, through its use of naval convention, conveyed its graphical authority; and second, as an intentionally evocative graphic that was intended to elicit a combination of sympathy and shock. The desired result of the diagram, driven by empirical evidence and emotion, was that the viewer would perceive the "inhumanity of the trade" through both the eyes and the heart, and prompted by the "instantaneous impression" that it made on the senses, be compelled to act.

At this juncture one additional point becomes important to say in words: these viewers, like the captives themselves, also had a race: they were white, predominantly British and predominantly men, with lives far removed from the experience of enslavement. In point of fact, Clarkson had an even more specific audience in mind with his design: the Members of British Parliament, who were scheduled to vote on a motion to abolish the slave trade in several weeks' time. One of the London Committee's own members, William Wilberforce, was among them, and he believed, and even said as much, that if the MPs "could actually see one thousandth part of the evils of that practice which they have, for so many years, under one pretense or another, been prevailed on to suffer to be continued," they would quickly commit themselves to the abolitionist cause.

Here is where we will return to the idea of the "god trick," mentioned earlier in this chapter, and explore its significance in fuller detail. The "god trick" is an idea developed by the feminist philosopher Donna Haraway, which they use to describe the false sense of neutrality that is conveyed through the default perspective of data visualization, the "view from above." The view from above can seem godlike—this is the "god" part of Haraway's term—but it is a "trick" because it preys upon our general tendency not to notice, let alone question, any perspective that adheres to the default. In this particular case, the seemingly godlike perspective is, in fact, the perspective of "predominantly white and male abolitionists and lawmakers," as sociologist Simone Browne observes. Browne analyzes Clarkson's "Description" in terms of the god trick, and employs it to underscore Haraway's primary point: while the "view from above" may seem like a view "from nowhere," it is in fact a view from somewhere—all viewpoints are. For Browne—and, we hope, for you now as well—the "Description" provides unassailable evidence of this fact.

Given Clarkson's own writing on the subject, he would likely not disagree. Clarkson celebrated how the chart "brought forth tears of sympathy in behalf of the sufferers, and it fixed their sufferings in [the viewer's] heart." But Browne's analysis of the power relations embedded in the "Description," and more specifically, of "the primacy given in these abolitionist texts to white gazes and vantage points to the trauma of slavery," pushes us as twenty-first century viewers to see more. Looking closely, she explains:

"One can see that each of the tiny black figures are not replicas of each other; rather, some have variously crossed arms, different gestures, or seem to turn to face one another, while some stare and look back at the gaze from nowhere, and in so being the Description of a Slave Ship can also be understood as depicting black looks and the trauma of Middle Passage as multiply experienced and survived."
Simone Browne

Did Clarkson intend to depict the captives looking back at the viewer, challenging their gaze? Or was it just that, in his commitment to accurate representation, he could not but depict the captives' resistance in ways large and small? These questions lack definitive answers, but their possibilities are what matter more. What would it mean to visualize the experience of the Middle Passage from the perspective of the captives themselves? Is this a task that should be undertaken, and if so, by whom? What data would be required? Or, in the absence of data, what information might be marshaled instead? Should the visualization by one that anyone could access? Or is there some knowledge that should be kept from public view?

These were the very questions that I, Lauren, brought to the Data by Design project team. I also brought a dataset: a full download of the Trans-Atlantic Slave Trade Database, which (as of the time of this writing, in Spring 2024) contains records of 36,150 unique slaving voyages that took place between the years 1514 and 1866, resulting in the captivity and forced migration of an estimated 10.6 million souls. Ever since the first release of the database, in 1999 via CD-ROM, scholars and designers have attempted to give this powerful data visual form. Perhaps most prominently, in 2016, Andrew Kahn and Jamelle Bouie produced an animated visualization of the data for Slate, the online magazine, which depicted each of the 20,528 voyages that were then in the database as small black dots that were seemingly pulled from the west coast of Africa to the Americas as if by magnetic force. While intended to "give sense of the scale of the trans-Atlantic slave trade across time, as well as the flow of transport and eventual destinations," the visualization was roundly critiqued by scholars of slavery for the god's eye perspective that it adopts. As literary scholar Britt Rusert asserts, "It's as if a series of ‘invisible hands' operate the trade," rather than specific people who should be condemned for their acts. Although she does not formulate her critique in these exact terms, what Rusert identifies is another version of the "god trick" at work.

Reflecting on this visualization in the context of the questions posed above enabled our project team to clarify our task. We first considered the provenance of the dataset, and reflected on the fact that the shipping logs and other data tables that served as its primary sources were created by the enslavers, and not the enslaved. This reminded us of the power relations embedded in the data, those that could never be removed, as well as of how that power contributed to a range of omissions and gaps. We also reflected on our own subject positions, and the fact that, among the five of us collaborating on this particular visualization, only one of us had ancestors who had themselves been enslaved. This prompted a recognition on behalf of the group that there were certain stories about the data that we could not tell, and should be left for others to convey. Finally, we reflected on Jessica Marie Johnson's powerful statement that "there is nothing neutral, even in a digital environment, about doing histories of slavery." This called us back to the range of harms that can be brought about by engaging with this history, as discussed earlier in this chapter, and to how data visualization is not immune. We saw the potential for "second-order violence," as Hartman terms it, both in the act of reanimating a dataset that, in its original form, conscribed the people it represented to living death; and in the act of controlling the layout and motion of this dataset which itself documented the forced migration of so many. From this process, our goal became more refined. In order to honor the enslaved as they lived, and not as they were reduced to data, we would need a visual strategy for showing just how much about these lives the data could not and could never show.

Variable nameDescriptionDerivation (if applicable)Start Date .The date that the voyage beganEnd Date The date when the vessel arrived at its destination.Total Embarked [IMP]The total number ofenslaved individualswho embarked on the voyage. Thisvariable is animputed variable.Total Disembarked [IMP]The total number ofenslaved individualswho disembarked atthe conclusion of thevoyage. This variable is also an imputed variable.ResistanceA binary variableindicating whetheror not a documentedact of resistance wasrecorded, with "1"indicating a record ofresistance.Mortality RateThe percentage ofindividuals who did not survive thevoyage.Derived by subtracting TotalDisembarked from TotalEmbarked and dividing theresult by the Total Embarked.DurationThe duration of avoyage in daysDerived by calculating thenumber of days between StartDate and End Dote.
Geological Investigation of the Alluvial Valley of the Lower Mississippi River, plate 22
usNumber of peopleat the beginning.Number of peopleat the end.If theduration ofthe voyage is+++ then theamplitudeincreasesus
The interesting narrative of the life of Olaudah Equiano, or Gustavus Vassa, the African , [frontispiece and title page]
Begin Voyage
End Voyage

One variable included in the dataset, labeled “Resistance,” seemed to hold the key to this work.

It contained seven categories for indicating the form of resistance that took place on any particular trip. Could we use the “Resistance” variable to create a visualization that, to recall Browne's phrase, “looked back at the gaze from nowhere”? We began by pulling out the voyages that had any form of “resistance” associated with them, as well as six of the more basic variables that were associated with each trip.

The additional variables we selected, the voyage's start date, its end date, the total number of individuals who “embarked” on the voyage, and the total number of the individuals who disembarked, would allow us to provide a basic picture of each of the 572 voyages that contained a documented act of resistance.

Because our initial motivation was to visualize the dataset from the perspective of the enslaved, our design departed from a frequent observation made about the experience of the Middle Passage: that the captives did not experience time as linear while in the hold of the ship.

Drawing visual inspiration from Harold Fisk's alluvial diagram of the Mississippi River, which, as artist and scholar Romi Morrison explains, “deemphasizes the linearity of the river” in favor of showing a comparative view of its various paths over time, we arrived at an idea to use bends and turns to represent the non-linearity of the Middle Passage.

We also kept the vertical orientation of the visualization so as to ensure that the viewer could not interpret the paths of the voyages as corresponding to any actual location on a map.

Borrowing the color palette from the Fisk diagram, but muting the colors so as to ensure that this visualization of an experience of trauma would not inadvertently become beautiful to perceive, we represented each voyage as a snaking line determined by the number of captives held on each ship.

In the final visualization, the width at the top of each “bind,” as we came to call them, corresponds to the number of captives who departed from Africa on each ship. The width at the bottom corresponds to the number who arrived in the Americas having survived. The duration of each voyage is conveyed through the amplitude of each bind, but plotted from the side.

While Fisk's original design superimposes the floodplains of the Mississippi from all points in time on a single image, we chose to retain the start date of each voyage, since the rise and fall of the slave trade—and the resistance that met it throughout—remained important for us to convey. Here the binds are arranged chronologically, from the first recorded act of resistance aboard a slave ship in 1565, through the last in 1865.

Since the majority of the voyages lacked data on the month or day of departure, we grouped the voyages by year. While the visual effect of this decision is not visible when viewing the voyages as a whole.

Zooming in on a particular time span exposes these clusters for closer inspection.

As an example, we might consider the time-span between 1756 and 1766, the decade during which Olaudah Equiano was enslaved. Within each year, we can also see that the binds themselves overlap—what is called “occlusion” in visualization design. While generally viewed as a design problem, and something to avoid, we made the decision not to further space out the voyages because of viewing them together communicates the collective force of these acts of resistance, as well as the additional nuance that a single inclusion criterion—resistance or not—cannot convey.

The voyage that took Equiano from Benin to Barbados and on to Virginia is not pictured in this chart, however, for it did not include a form of resistance that was documented in the database. But it might have been included among the 35,504 additional voyages that the database currently contains.

With the additional voyages also plotted, the binds transform into life-affirming arteries within the sinews of human flesh.

But as evocative as this visual representation may be, there are many other forms of resistance, large and small, that this visualization does not convey.

In his autobiography, for example, Equiano recalls observing acts of resistance aboard the ship that were set in motion, but ultimately “prevented by the ship's crew.” These acts of resistance likely had concrete effects, both for the crew which—in their need to suppress them—perhaps also attuned them to the odious nature of the acts in which they were engaged; and for the captives, who perhaps might have taken heart—or inspiration—in the possibilities to push back against their likely fate. But as unfinished acts of resistance, they would have gone unrecorded in the dataset.

We might also consider the myriad number of smaller acts of resistance, including those in which Equiano himself engaged. Upon first being captured, for example, Equiano described how he refused to eat; and when his captor attempted to give him a new name, depriving him of his identity and his Ibo roots, “I refused to answer to my new name,” Equiano explains. Equiano's more “quiet” forms of resistance, as Kevin Quashie might term them, were also real, and also meaningful, even as they remain difficult to represent as data ever at all.

It was here, again, that we turned to the power of data visualization to bring these quiet acts of resistance to light. In the final view, we display all 36,079 voyages with a color fill, implying that every single journey involved acts of resistance—some that are recorded in the dataset, some that took place but went unrecorded, and some that defied recording at all. What we were visualizing, our process allowed us to see, was not actually the slave trade, but the data it had left in its wake.

But as the additional voyages are layered into the frame, the viewer can no longer see clearly enough to deduce anything about a specific voyage. This is intentional, because the insight that we seek to prompt exceeds the data on display: that there are certain phenomena, such as the slave trade itself, which we can never fully understand.

While it would take another nine years—and, according to the Trans-Atlantic Slave Trade Database, an additional 1.5 million people or more forcibly separated from their homelands—for the British Parliament to formally abolish the slave trade, historians generally credit "Description of a Slave Ship," and Thomas Clarkson in particular, for a large part of the campaign's success. Clarkson himself likely contributed to this narrative; in 1808, one year after the formal Act of Parliament, he published a two-volume tome, The History of the Rise, Progress, and Accomplishment of the Abolition of the Slave Trade by the British Parliament, which provided his own first-hand account of British abolition.

Interspersed among the History's nearly 1,200 pages were four images—among them, a revised version of "Description of a Slave Ship," and a new visualization that Clarkson himself designed. It depicts the history of abolition in the form of a watery network. Each of the "springs and rivulets" is labeled with the name of a significant abolitionist. The streams are arranged from top to bottom, roughly according to time, with horizontal lines separating efforts that took place before 1650, 1700, 1740, and 1787, respectively. As the viewer follows the streams down the page, they converge into "two great political rivers, representing the abolitionist movement in England and America," and while outside of the bounds of the page, presumably meet in the sea.

A “stream chart,” or a map-like graphic that resembles water flowing downstream from the top of the page to the bottom, the metaphorical “rivers” growing in size and connecting as the viewer’s gaze travels downward with the water. The graphic is symbolic rather than concretely illustrative of particular waterways, for its connection to famous (albeit arbitrarily named) abolitionists is fluid, emphasized by the curved, bent, and swirling paths of the tributaries. While to Clarkson the diagram shows a watery path, the chart also resembles trees due to its brown color and rigid shapes, as if two sturdier trunks hold up the multiple diverging, splitting branches. While most of the branches or smaller rivers have abolitionist names associated with them, many of the cross-sections are also labeled with a letter from the English alphabet in, again, a seemingly arbitrary manner. The two bottom “trunks” or grander bodies of water at the bottom of the page are labeled X and Y (to the left and right, respectively), while the cross sections of the rivers that flow into both the X and Y rivers are labeled E and, just slightly above, C.
A diagram of the British and American abolitionist movement, depicted as a set of rivers and tributaries, created by Thomas Clarkson to include in his book, The history of the rise, progress, and accomplishment of the abolition of the African Slave-trade by the British parliament (1808). Image courtesy of Wikimedia Commons.

On the surface, the metaphor of abolition as a network of streams and rivers flowing into a common sea may seem like an apt representation of a social movement which drew strength from countless individuals and collectives over an extended period of time. This resonance must have been intentional, given how Clarkson elsewhere analogized the British antislavery movement to the distributed functioning of a human body, with "every limb... essentially necessary for the completion of a perfect work." And yet, certain key contributors are missing from the chart. Most notably, the name of Olaudah Equiano, or of any other Black abolitionist, is nowhere to be found.

As with "Description of a Slave Ship," the question of audience returns to the fore. This chart was also not designed for those who were enslaved, but rather, for a white British viewership—those who sought to valorize their own role in the fight to end the slave trade. In his analysis of the image, Marcus Wood speculates that this goal—and its disconnection from the actual facts—is the source of the confusion that the visualization ultimately imparts. Clarkson's "attempt to create a self-sufficient cultural history for the cause requires a coherent descriptive model which is capable of overriding the heterogeneity of the names and writings he has furnished" in the text of his volume, Wood asserts, as it does of the composition of the movement overall. Here, the success of the movement "belong[s] to no single abolitionist but to a mysterious sea, into which, in a strange reversal of the generative metaphor, al`l the tributaries pour." The sea metaphor is further clouded by the role that actual water—namely, the Atlantic Ocean—played in the slave trade. Why would Clarkson use water—the very site of the dehumanization that enslavement brought about—as the anchoring metaphor of his account?

But Clarkson was anchoring his diagram in some stable ground: namely, the then-prevalent use of water and streams to visually represent the passage of time. In Cartographies of Time, Daniel Rosenberg and Anthony Grafton position Clarkson's diagram as a direct adaptation of the ideas expressed by the German chronologer, Friedrich Strass, who had published his own widely circulated "Strom der Zeiten" (Stream of Time) only a few years earlier, in 1803. Translated into multiple languages, including English, and widely circulated across Europe and the United States, "Strom der Zeiten" was almost certainly a chart that Clarkson saw. But even if he did not, Clarkson clearly intuited how the water metaphor "gives greater liveliness to the ideas, and impresses events more forcibly on the mind, than the stiff regularity of the straight line," as William Bell, the English translator of Strass's chart, explained.

A “stream diagram” written in German that depicts major historical events, eras, and empires across the globe, colored according to region and pictured as water flowing from grayscale clouds at the top of the page. Each stream, which oscillates in size and merges with surrounding paths, contains small script detailing various leaders and conquests as time goes on “downstream.” The colors are predominately dull reds and blues––fading into the bland beige color of the paper––with only subtle differences in tone between them. The vertical borders of the chart, the left and right sides, show increments of time beginning hundreds of years back B.C., to the beginning of the nineteenth century when Strass composed the chart. Each stream descends to the bottom of the page where a different country is labeled beneath its cutoff.
Strass’s “stream diagram” translated from German to English. In contrast to the original, this chart is vibrantly colored, with bright yellows and light pinks and reds standing out against the paper’s color. The clouds heading the page remain grayscale, but the border is green instead of the faded beige tone of Strass’s original. Also unlike the original, at the bottom of the page, beneath the streams, two paragraphs offer an explanation for what Strass calls the “universal history” of the world.
An early and influential "stream diagram" created by Friedrich Strass in 1803. The diagram was translated into mulitple languages and became a model, in both Europe and the United States, for how chronology might be depicted. Image courtesy of the David Rumsey Map Collection, Cartography Associates.

Indeed, there is a version of the history of data visualization that need not be significantly reconfigured in order to provide Clarkson with a more prominent place. Many scholars, including Rosenberg and Grafton, have made the case that chronological charts such as those created by Strass and Bell, as well as their more linear antecedents, "cleared the way for statistical graphics" by introducing the idea of consistent scale. This argument is confirmed by the purported "pioneer" of statistical graphics himself, William Playfair, the subject of the next chapter, who praised the genre for "making space represent time," and for using "a line of proportional length and in a suitable position." As we will learn, Playfair described the purpose of his own visualizations in terms quite similar to Clarkson's: to unite "a number of separate ideas… under one simple impression of vision, and consequently, one act of memory."

But to simply slot Clarkson into the standard history of the field would miss much of the point. For Clarkson's visualizations, both "Description of a Slave Ship" and his map of abolition, matter as much for the questions that they provoke as they do the knowledge that they reveal. When we look closely at either the diagram or the map, we are prompted to ask what this "impression" conveys and what it omits. We must consider the perspectives of the people for whom these charts have been designed, the people who will benefit from looking, and the people who are merely looked upon. We must consider whose data is on view in any particular chart—and in the case of "Description of a Slave Ship, whose actual lives. And we must consider the potential for violence or harm that visualizing their data might, however inadvertently, bring about. These are not questions that Clarkson himself brings to the fore, but they are ones that we as twenty-first century viewers of his visualizations—and as designers of visualizations as well—should now be required to ask. If these questions seem weighty, it is because they are. Visualizations of data are indeed powerful, as the success of "Description of a Slave Ship" affirms. But it is precisely because of this power that we must continue to probe the nature of the insights that visualization can help to prompt, and the additional insights that it can never convey.

We will never know if these are some of the questions that Equiano posed to Clarkson upon seeing the original diagram, as there is no record of the conversation that transpired. Several weeks later, however, Equiano published a letter in The Public Advertiser, a prominent London newspaper, in which he acknowledged "having seen" the chart. Interestingly, Equiano does not comment directly on the image, choosing instead to affirm the work of the abolitionist movement overall. But I believe that we can still learn from Equiano's statement about what he saw. In the diagram, Equiano saw clear evidence that its designers sought to "contribute to so important a moral and religious duty as that of" ending the slave trade. But he also saw that the chart alone would not be enough. As a person who had himself been enslaved, Equiano understood first-hand that ending "one of the greatest evils now existing on earth" would require more than the chart alone could convey. And therein lies the final lesson of "Description of a Slave Ship" for visualization in the present. It has to do with the continued insistence that before there is data, there are people—people with lives that data alone cannot convey. It also underscores how, if the goal of a visualization is to bring about change, then it must necessarily be accompanied by action. To be sure, not all visualizations are designed to effect political change. And in fact, most visualizations are explicitly designed with the opposite goal—of focusing on what the data, itself, can reveal. But the example of "Description of a Slave Ship," which visualizes the most monumental of humanity's stakes, should underscore the responsibility that comes with the design of any visualization—and with the viewing of any visualization as well: to ask what knowledge it can point towards, and what it cannot show.

Conceptual takeaways

  • Always recall the power of visualization
  • Ask for and by whom any visualization has been designed
  • Consider the context of the data—including any people behind it
  • Remember that there is always more than data alone can convey

Practical takeaways

  • Consider the tradeoffs between efficiency and detail
  • Ask who will benefit from your visualization and who might be harmed
  • Probe any missing data and the reasons why
  • Hold space for the possibility of not visualizing at all


  1. Carretta, explain evidence to doubt veracity of childhood in Africa.
  2. Equiano 55, 58.
  3. Say it out loud. Contemporary CS acronyms have nothing on C18 abolitionists!
  4. The art historian Cheryl Finley, in her landmark study of this image, Committed to Memory: The Art of the Slave Ship Icon, makes clear that it’s important to identify which version Equiano saw. In particular, this was a print accompanied 4-page pamphlet. Later, the Plymouth Committee printed them together as a broadside. Finley also powerfully considers the impact of this request from Equiano’s perspective: “One can picture how [Equiano’s] eyes might have followed the contours of the darkly shaded figures, counting each one, possibly imagining the face of someone he once knew. Fine black lines representing the wall that divided groups of figures by age and sex might have caused him to pause and think about which space he had occupied or the people who had lived and died next to him. The combination of rows and rows of black figures separated and surrounded by fine black lines schematically mapped the space of the hold, marking a route to untold horror” ##.
  5. Equiano 58; add in more on Cugoano refusal, p. 15, connect to data refusal.
  6. Clarkson, History
  7. Note about centrality of impression, Locke, senses, Schuller, Biopolitics of Feeling. Also Hume, impressions vs. ideas.
  8. Finley 34.
  9. Hartman, Scenes.
  10. Hartman, Scenes.
  11. Morgan, Reckoning with Slavery.
  12. Spillers 72. Also gloss critique of white space / modernism.
  13. Cite discussion in intro.
  14. Spillers
  15. Finley makes a similar point with respect to another diagram of the Marie Seraphique. (Note that both images are in high circulation because of the process of amends-making by the Musée de Nantes)
  16. Gordon Wood elaborates this point: “This image supports an abolitionist cultural agenda which dictated that slaves were to be visualized in a manner which emphasized their total passivity and prioritized their status as helpless victims” (17). Can also gloss body vs. flesh, Spillers, Tiffany King, Wood 28.
  17. Explain connection to Hurston, Ligon, “Against a sharp white background,” and Senchyne/Fielder book. Bernier also lends her support to this interpretation: “Working not to humanize but to propagandize black subjects bought and sold into slavery, the iconographic emphasis across these broadsides betrays a white British commitment to exposing slavery’s atrocities by imagining black women, men, and children not as individualized subjects but as unindividualized objects defined solely by their incarceration on board a slave ship” (998).
  18. In fact, Otto and Marie Neurath, the inventors of the ISOTYPE icon system, incorporated their isotype icons into a reproduction of the diagram in their pamphlet on the history of global trade. They also held a ca. 1800 version of the diagram, created by the German printmaker Jacob Xaver Schmunzer, in their personal archive. It is possible to make an argument their icons, like those on the slave ship, were intended to serve as abstract representations of “observed particulars”—in their case, of the population of the world. What’s more, they similarly sought to enlist their icons in a political cause. [ADD IN IMAGE HERE]
  19. Tufte
  20. Viegas in Data Feminism.
  21. In an example of mixed methods research avant le letter, Clarkson also published the transcripts of his interviews with these men at roughly the same time as he released his revised version of the Plymouth Committee’s “Plan.” For more on the interviews, see Riedeker 319-324.
  22. Cite chart, transcription in Finley 62-67. Clarkson, para 1.
  23. 27. Ref Marey. Also note about definition of visualization.
  24. Wood 28
  25. Wood
  26. Clarkson’s motivation for these design choices is, admittedly, difficult to discern. Why leave the women unbound when evidence points to the fact that they were also “known to organize, lead, and assist with rebellions aboard slave ships,” Finley wonders (59). Is the exaggerated sexuality of the women figures a comment, on the part of Clarkson, about the “objectified status of the black female body and the history of rape and sexual abuse to which black female slaves were subjected by their white male captors,” or because of his own racist perceptions about the sexuality of Black women, Finley further enquires (59). We may never be able to answer these questions with any degree of certainty, but their possible answers expand our understanding of the chart nonetheless. More specifically, they underscore the perspective inhabited by the chart, and point to the additional perspectives we must consider if we are to achieve a more complete picture of the actual subject at hand.
  27. Here, Ian Baucom argues, Clarkson mobilizes a central tenet of the Scottish Enlightenment, which held that meaning was created first by verifiable evidence and then through a responsibly used imagination. In this case, Clarkson enlists the “facts” of the slave trade in the interest of engaging the “otherwise disinterested spectator in the sufferings of an actually unseen other” (Baucom ##). But for this transformation to take place, the viewer would be required to enlist their own imagination in imagining the suffering of others.
  28. Add in Clarkson quote. Para 22.
  29. Quoted in Baucom 218. Also ref wood model, and discussion in Critical Visualization book.
  30. Haraway, D’Ignazio and Klein.
  31. Browne 49.
  32. Haraway.
  33. Quoted in Baucom 267
  34. Browne 49. While on this note, Clarkson would also likely not disagree. In the History, Clarkson proudly recalls how the chart “brought forth tears of sympathy in behalf of the sufferers, and it fixed their sufferings in [the viewer’s] heart.” Quoted in Baucom 267
  35. Browne 50.
  36. The viewers intended to be affected by this image were white abolitionists, and the response that was intended was one of imaginative, sympathetic response. Clarkson himself frames the value of the image in these terms, recalling how “No one saw it but he was impressed. It spoke to him in a language, which was at once intelligible and irresistible. It brought forth tears of sympathy in behalf of the sufferers, and it fixed their sufferings in his heart” (##). Here, Ian Baucom argues, Clarkson mobilizes a central tenet of the Scottish Enlightenment, which held that meaning was created first by verifiable evidence and then through a responsibly used imagination. In this case, Clarkson enlists the “facts” of the slave trade in the interest of engaging the “otherwise disinterested spectator in the sufferings of an actually unseen other” (Baucom ##). But for this transformation to take place, the viewer would be required to enlist their own imagination in imagining the suffering of others. As Finley also explains, “The image is a starting point for the viewer – a point of reference while the text enables the reader to elaborate on the image in her mind” (##).
  37. Add in cites to TAST database, history, and overview.
  38. TAST, “History of Project”
  39. As Britt Rusert helpfully summarizes, “The Slate map has at least two direct antecedents: a set of maps of the slave trade on the Trans-Atlantic Slave Trade Database website, and David Eltis and David Richardson’s 2010 print volume, Atlas of the Transatlantic Slave Trade, whose maps were “constructed from a set of estimates derived from the Trans-Atlantic Slave Trade Database as it existed in January 2008— almost a year before the launch of the Voyages Web site” (xxiv). These earlier iterations of maps derived from the Trans-Atlantic Slave Trade Database are a reminder of the important continuities between the “age of print” and the “digital age.”
  40. Ref Rusert, “New World.”
  41. Ref Johnson, “Markup Bodies”
  42. Spillers, 1978; Hartman, 2002; Sharpe, 2016; King, 2019
  43. Morrison 2018.
  44. A further connection to Spillers’ theorization of the process of dehumanization as the conversion of bodies into flesh that the Middle Passage brought about.
  45. First quote is ch 2, second ch 3. Need numbers.
  46. Add in note about wide circulation, in England France and US. Finley chapters 2 and 3.
  47. “I was in possession of more facts on this subject than any other person,” as he wrote in the second chapter of the 1200-page tome (Clarkson, History, vol 1, p 31) Clarkson, History, vol 1, p 31.
  48. Cartographies of Time.
  49. History ch 12.
  50. In adapting this particular style of image, the hydrographic map, to the abolitionist movement, Clarkson also imposes the colonial valences of mapping—and mapping waterways in particular—onto the abolitionist movement. Here, however, it is not the discovery of new trade routes, but the discovery of the horrors of slavery, that the image renders visible; and these horrors were, of course, already viscerally known to those who experienced the trade’s direct effects. Wood 4.
  51. Wood 4.
  52. Strass “believed that a graphic representation of history held manifold advantages over a textual one: it revealed order, scale, and synchronism simply and without the trouble of memorization and calculation,” Rosenberg and Grafton explain (Cartographies of Time 143).
  53. Bell, quoted in Cartographies of Time, p. 147.
  54. Cartographies of Time 136. Also gloss contribution of Priestley.
  55. Quoted in Cartographies of Time 136.
  56. Ref Playfair, “Introduction,” x. Also cite Clarkson, second version of his goal: to “bring [the history of abolition] before the reader, that he may comprehend the whole of it at a single view.” Playfair also uses the phrase “single view” in the title of his book.
  57. Ref Norton edition, p.205.