Extruct map data from - https://www.openstreetmap.org/ in .OSM files
Convert .OSM files throuth OSM2World in .OBJ files
Import .OBJ files in 3d software (i use 3ds Max)
For detaching objects into separate groups (buildings, roads, rivers...) use [script for 3ds Max](http://www.scriptspot.com/3ds-max/scripts/detach-by-material-id).