The amount of water on earth a. increases slightly over time changes forms. b. decreases slightly over time and does not change form. c. remains the same just in different forms. d. remains the same and does not change form.

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?