How: Actual map for 2D Game

If Anyone could point me in the direction of how to use A gps app for the map of my game I would be most appreciative.

For Reference to what EXACTLY It is I am looking for there is a game called mission chief that uses leaflet & openstreetmaps as a game map to place buildings (fire stations) in a real world 2D map and uses it to generate calls for the stations at real world locations.

This is as close to exactly what I'm looking to do as it could really get and all tutorials I can find after 3 days of searching are on 3D maping.

 

That's my question too.