Cool project - and I like that it uses USGS hydrography data.
They publish all kinds of terrain survey information about the entire USA for free. There's probably enough data to make your own GPS mapping device/app.
They publish all kinds of terrain survey information about the entire USA for free. There's probably enough data to make your own GPS mapping device/app.
https://www.usgs.gov/mission-areas/water-resources/science/s...