What did the countries in the triangular trade do?

Over half of the african-american population in the united states live in

Where the main factor that enabled the growth of cities and civilizations was the existence of

This is a 2017 topographic map of puerto rico in the united states, and i'm sorry that people there have suffered such a disaster. i want to ask, what do the yellow dots and areas represent on this graph? and the blue area and the little blue circle, and the little blue sign that looks like a signal tower, what do they stand for?