If you're using a smartphone-based GPS, use the HERE Maps and HERE Drive (from Nokia, actually), available on Windows Phone, Android and iOS. You can download the maps (globally, by the way, or US by state) so you don't eat up your data plan or rely on the sometimes spotty cell/Wi-Fi coverage, and it has full POIs including rides inside the parks and will do walking directions as well as driving, and they're working on incorporating the WDW transport system as well. WDW is particularly well covered as the roads have been entirely GPS documented.
Newer Garmin GPS units use the same mapping data, so if you have a new-ish one, update your maps and you'll be good to go.