Humans have been conducting censuses for 5000 years. You’d think they could get at least a ballpark within 10%, but then those censuses were conducted by societies with some semblance of productivity. There are likely thousands of people living in tribes in South America, Africa, and parts of southeast Asia that we don’t even know exist.
A satellite can identify a single marijuana plant in a forest. It does that by analyzing the spectrum of reflected light. That same satellite can spot the heat signature of individuals in a jungle, forest, or even through a roof. Given that satellites provide full coverage of the Earth every few hours, I suspect they know where people have collected.