Map page on this screen (Garmin CityNavigator) is the same location as the map screen in
>>874425, only difference is that >pic related has CityNav loaded.
>Some free optionsGPSFileDepot dot com, if there's something useful that fits your needs on there, free is a good price.
Coverage/consistency may be hit-or-miss depending on how much area you want in the map. Manufacturer's maps are better at that, especially at a country- or continent-wide level.
GPS still functions the same with additional mapsets loaded, you just have a better library for roads (name, where they go, type of road (highway, side-road, trail)) and points of interest (food, fuel, hotels, auto service/repair, shopping, etc).