Options vary from ArcGIS to OpenStreetMap to Natural Earth, Demographia, and Simplemaps. An index of up-to-date available global/world metadata from the World Bank, UN and others. Of these, simplemaps (world cities database) might have the easiest data format to pricing scheme.
Input data peer information is: country iso 3 code, city name, latitude and longitude.
Query data requirements are: population density, country iso 3 code, city name in UTF8, latitude and longitude. Some way to represent in C++ or query mysql database from C++ objects.
