If you're on Prince Edward Island, Canada, this app uses the location of your device to calculate what lot (or "township") you're in. There are 67 lots and three "royalties" (Charlottetown, Georgetown and Princetown) originally laid out by Samuel Holland in 1765. While they are largely no longer in contemporary use, they are irrevocably imprinted on the Island landscape, through the shapes of roads and property lines.
The app will look up your location, and either (a) display the number of the lot you're currently inside, (b) tell you it can't find your location or (c) tell you that you're not on Prince Edward Island (which might be true if, for example, you're on a beach or a bridge, all appearances to the contrary).
As long as you have the app open, it will continue to update the lot number, so if you go for a drive in the countryside, you can watch it update as you cross lot lines.
The app will also remember which lots you've visited, and will colour-code these in red on the map.