What's the creative idea to check the level in the wide area ?

Start, you need to have at least one or two bench marks (BM) inside or outside the target area. It is important to close-on the same BM or to another BM.

Then, it is important to establish a line of group of BMs inside the area, calculate accurately the levels of those points.

After that, you can simply start your project to cover all the area levels by starting and closing on those points that you had created.

if you have GPS , you will know every thing you want , or ask about all the information about this area or another area near to your wide area

Pertaining to the question on social condition of the people you must have to conduct census, and talking of wide area you must have to collect all data to gather information.