It's a shame that it stops at 1860 -- since a major part of the article is about how it was not primarily North America that was the recipient of slaves, but 1860 is the beginning of the Civil War (which concerned just the US).
Also would have been nice to show 'events', such as the banning of importing slaves to the US in 1807 (you can see the boat traffic essentially stop to North America at that point).
While there were sporadic slave ships making the crossing after 1860, the trade was already illegal in all destinations. This meant that unlike for the period during which the slave trade was legal, we have no surviving records of them.
From the FAQ for the database which it visualizes:
"For the Voyages Database, the time frame is set by default to the period from 1514, the first year in which a slave voyage can be documented, to 1866, the year of arrival of the last three documented slave voyages."
I don't know what accounts for the 6-year discrepancy there, but I would wager that the choice of ending in 1860 is not due to the US Civil War.
Also would have been nice to show 'events', such as the banning of importing slaves to the US in 1807 (you can see the boat traffic essentially stop to North America at that point).