Why do you have doubts? There are probably thousands of social science and public health studies that use mapping methods and analysis. There are many things that could be examined geographically.

Sir , so when the list of population is unknown can we use mapping technique for sample selection ?

The world is a very big place - we can be more informative if you state the general extent of the area of interest, the rectangle of minimum and maximum latitude / minimum and maximum longitude, or by administrative are ( rural, village, city, province, state, continent, etc. ).

There are datasets like Urban-TEP built environment land cover ( https://www.dlr.de/eoc/en/desktopdefault.aspx/tabid-9628/16557_read-40454/ ), the

GHSL - Global Human Settlement Layer gridded population ( https://ghsl.jrc.ec.europa.eu/visualisation.php# ), economics Dryad ( http://datadryad.org/stash/dataset/doi:10.5061/dryad.dk1j0 ) - these are well documented and their methodologies ad original source data and citations can point to other more specialized and localized sources as well ( https://www.microsoft.com/en-us/maps/building-footprints ). Some are also time series as well.

These were created because of the harmonization, lack, frequency, and quality of national census in many parts of the world.