Hello. You did not present the map to which this question refers, which makes it impossible for it to be answered accurately. However, I will try to help you in the best possible way.
The biggest center of the slave trade was Zanzibar, in West Africa, where the majority of Europeans moved to buy slaves at very low prices for themselves or to resell in European and American countries. In the USA, New Orleans became a center for the slave trade, while in Europe, England had large centers such as London, Brisol and Liverpool.
