An isodemographic map is a map that is drawn to represent populations of a certain area instead of by region, by borders, or by mountains or other common traits that maps are made by. The map that is given as an example with this question is a map of the world according to its population. So, you can see that the United States of America has more people than, say, England.
There are a more lot people in China than in the United States, but because they’re all concentrated in the coastal area of the country, it makes sense that the country is a little more squished than the United States. The middle of Africa, on the other hand, is an incredibly inhospitable space, so few people live there.