In addition
Possible Filenames for 3D Building are gmap3d.img and gmap3d1.img.
You can rename a map also to gmap3d.img and gmap3d1.img if you don't need 3D Buildings, so u have 2 additional map possibilities on your device.
This works only with Nuvi which has the capability to display 3D Buildings
These are the Nuvi 7x5 series and the 3790T