Planwise uses data from 3 different sources:
Map data for country administrative regions
Uses sources from https://gadm.org/
Friction map for coverage coverage
Coverage is calculated using the Google friction map it's a map that considers friction surface and enumerates land-based travel speed for all land pixels between 85 degrees north and 60 degrees south.
It combines different datasets (roads, railways, rivers, lakes, oceans, topographic conditions, land cover types, and national borders) every pixel is allocated a nominal overall speed of travel based on the types occurring within that pixel.
Population raster
From Worldpop this is the best available source for the raster population across the world. Planwise uses an UN-adjusted forecast for each year, adjust methods are described here
The technical document describes how to load new population information into Planwise