For PC users, you can remove the map's blur and clouds, allowing you to see more detail (and roads; well ones that aren't covered in snow anyway) by adding this to your Skyrim.ini (not SkyrimPrefs.ini!) file:
[MapMenu]sMapCloudNIF=0bWorldMapNoSkyDepthBlur=1fWorldMapNearDepthBlurScale=0fWorldMapDepthBlurScale=0fWorldMapMaximumDepthBlur=0
If you want to zoom in further, and rotate in full 360 degrees, add these lines under [MapMenu]:
fMapWorldMaxHeight=130000.0000fMapWorldMinHeight=150.0000fMapWorldMaxPitch=360.0000fMapWorldMinPitch=0.0000fMapWorldZoomSpeed=0.3500