How is the GDP of a country calculated like is a research conducted or a survey done or something else?

Iam stuck on this question! 45 points : ) how do increases in temperature affect the density of ocean water? answer choices: (a) density does not change (b) density increases (c) density becomes variable (d) density decreases

How would i answer this for an exam?

The map above shows where people live in the united states. areas that are darker blue are areas where people live close together. areas that are lighter colors are places where people live farther apart. as a geographer, if you were to study where people live and why they choose to live in these places, which of the six essential elements of geography would you be using?