Once you have downloaded the app and an area on to your mobile device (we recommend WiFi) you will not need mobile/cellular data in order to use FATMAP. GPS functionality does not use data.
The only function which does need data is the real-time location sharing and external links such as the weather and avalanche forecast.
To update the app with the latest user comments and conditions you will need data, but this can be done over WiFi if you do not have data enabled.
Streaming maps requires an internet connection, you will need to upgrade to premium to download maps to your device.