Some mapping apps (including Google Maps) do have an option to download your local map data (presumably when you're on WiFi) so you don't have to download it via your data plan. You may be able to configure your app to not use any other data (eg not uploading anything until you're back on WiFi). You can also just switch off your data plan if you really don't want to use data. Some GPS apps will continue to work fine with the data switched off, especially if you have already downloaded the maps.