What are some of the factors that could contribute to an area being sparsely populated?

The red square is a famous historical site that is located in

Can someone me choose a broad topic and area of focus i am really doing this as a tally to see which one most people pick ok water pollution global warming endangered species atmosphere for the !

What does 2[tex] {2}^{ - 4} \times {2}^{ - 2} [/tex]