Location calculation is done onboard and works without network connectivity. The cell-tower based lookup for your current location is implemented via a included binary cell database extracted from OpenCellID.
This "NetworkLocationProvider" works without network connectivity and will never post your data anywhere. You are thus encouraged to help OpenCellID to gather more cells in order to improve this project.
Keypad-Mapper 3 can be used to gather cell information for OpenCellID.
Warning: This app drains battery and seems no longer maintained.