All modern GPS receivers have SD/microSD card facilities so that users can store proprietary maps, custom maps, routes, tracks, waypoints etc as required. Proprietary maps (such as the Ordnance Survey Discoverer maps sold by Garmin) are usually supplied on SD cards ready to insert into the device. Custom maps and those from suppliers such as Talkytoaster usually take the form of downloads which have to be transferred to a blank SD card provided by the user.
We suggest that any SD/microSD cards purchased for use in a GPS are “industrial” rather than “consumer” quality, not least because they are generally more reliable especially in high and low temperature environments. There is an additional cost of course, but this is modest in relation to the cost of the GPS receiver itself.