#BlackHistoryMonth | Transatlantic Slave Trade

“Perhaps the most worrying legacy of African slavery in the New World is the persistent oppression of all people of African descent in the Americas. A recent quantitative study shows that up to about 1820, approximately five Africans were brought to the New World for each European migrant. But in the course of the nineteenth century all that changed, as the booming American economies attracted free migrants from Europe. This means that the African slaves did the back-breaking work, but as the fruits of this work began to mature others came in to reap the harvest, with the blacks continuing to be held back in bondage. Even after emancipation, legal and other forms of oppression still blocked black access to power and resources. Thus the process of capitalist accumulation passed them by, giving rise to a black population in the Americas generally characterized by poverty, extreme deprivation, lack of education, disease,”

― Joseph E. Inikori, The Atlantic Slave Trade: Effects on Economies, Societies and Peoples in Africa, the Americas, and Europe


Black History Month is meant to be a time to reflect on the history of America and the monumental impact that Black Americans have had in the formation of our nation. Part of this both wonderful and tragic history is the acknowledgement and conversation about how Black Americans arrived in this country. They did not choose to come here. They did not come here to pursue a better life, or to find better opportunity, or to flee persecution like every single other people group came here to do. Instead, they were brought here as cargo, forced to work the fields and factories without pay to produce the richest country the world has ever seen, only to be second class citizens in the country they created. This topic, however uncomfortable, was the driving force behind my new visualization, The Trans-Atlantic Slave Trade.

This is such an important topic to really think about as it has shaped almost every aspect of the world we live in today from what countries are in power, to the socioeconomic status of black people around the world, to the social construction of race and the eugenics that reinforced those myths. As I made this dashboard, I tried to make sure I treated every data point as a person, and admittedly, at times I got emotional. At times I was moved to tears, at other times I was angry, and for the rest of the time (the majority) I was simply inspired by the perseverance of Black Americans.

The biggest time spent on this dashboard was researching the different locations to geocode the locations that the original batch geocode had gotten wrong. Many of the locations were names of old colonial forts or settlements, so the current Google Maps did not have these locations stored. The deeper and deeper I read about all of the stories and historical accounts I came away with a resounding takeaway…the Trans-Atlantic Slave Trade influenced almost every single aspect of the world we live in today.

The food you eat. The music you listen to. The language you speak. The socioeconomic patterns of your country. Your religion. The sports you play. Almost EVERYTHING you can think of can be traced back to this dark chapter of human history. Also, I figured #BlackHistoryMonth would be a good time to release this dashboard, even though I think we should be more open to talking about the long lasting effects of slavery and colonialism the other 11 months of the year, but that’s just me…

Building the Dashboard

All of the data collected for this dashboard came from slavevoyages.org. They have an amazing database of voyages made during the Trans-Atlantic Slave Trade for you to search through. The only thing that was missing was the specific lat/long of each location. I began by running all of the Places in the data set through a batch geocoder online. Then I plotted those points, colored them by stage in the trade, then determined which locations seemed off due to geography. For the locations that seemed to be incorrectly geocoded I went back, sometimes having to read through old books and historical articles online, and found the current day locations that some of the places were referring to. I probably did this for around 300 locations, so it took many hours to compile the accurate latitude and longitudes, but it was a labor of love.

Once the lat/long data was collected I had to decide what method I would use in Tableau to map the points, MAKELINE() or a good old fashioned UNION ALL and path. After trying both, I realized that I needed to make a data set where I could plot all of the points and have shapes on both ends of the line, as well as have the curved line feature of MAKELINE(). This called for Tableau Prep.

The original data was presented as each row representing one voyage, so it included the place of origin, people purchased, and ending. This made the data appealing to the MAKELINE() method, but because I wanted to combine the two methods I first needed to stack the places vertically with only one lat/long column. This was done with the flow below.

I then created the final data set by bringing in the Lat/Long of the different locations to each of the columns representing each of the places in the voyage. I then Unioned the previous data set to this one so that I had a MAKELINE() capability and the path capability. The one shortcoming I found using MAKELINE() was that when I filtered for a line that there was only able to be a shape at one end of the line, not both. I could totally be wrong here, but please let me know!

To create the filtering action I made a Blank Parameter, aptly named [Blank Parameter]. I then used the formula below to enable a Parameter Action (dragged to Filter and set to “True”) that shows all of the connected voyages to the place that you click on.

Creating the viz itself was pretty straight forward. Once the data was structured properly, all you had to do was create the plots for the MAKELINE() fields and drag them to the marks card. Then, you have to create a dual axis and drag the indicator of the voyage plots into the marks card. Creating the text and overall messaging was one of the toughest part. For feedback on that, I leaned heavily on Candra McRae, Chantilly Jaggernauth, Luke Stanke. Their advice in terms of messaging and color scheme was invaluable. Thanks to you three.

Take Aways

This dashboard is heavy, but it was intended to be. This is not a fun topic for anyone, white or Black. But these are the topics I love writing about, the ones that make you squirm in your seat a little. The ones that make you think a little bit more about yourself and how you fit in the world around you. I love challenging assumptions and way we view the world. My hope is that this dashboard gets viewers questioning things about themselves, their countries, and the world in general. Enjoy, and thanks for reading!

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