GPSes are becoming commonplace, not just as the standalone devices we have in our cars, but perhaps even more often as a capability built into our smartphones. In the majority of cases, the data that those GPSes generate is used by and stored in the device itself, but occasionally people want to access that data in other ways. A typical instance is when someone wants to download waypoints, routes, or tracks for use in computer-based mapping software or to transfer data to another device. In such cases the appropriate GPS interface sometimes is RS-232 serial. For example, a number of Garmin GPSes have serial output:
Garmin stuff is pretty rugged and this unit is used in a car, not clamped to my handlebar like my Garmin GPSMap 60CS, which has been jolted for thousands of miles in heat and pouring rain.