I am a new user and have downloaded a topo map to my computer and want to load it on my new etrex 20. can I load it to a micro sd card and then just put it in the etrex? How do I load the map to the etrex without erasing the worldwide map that came with the unit.
Garmin's software is smart enough not to delete your basemap. You can use either a card or internal memory for the map. First you must install Basecamp. http://www8.garmin.com/support/download_details.jsp?id=4435
Then see this tutorial: http://www.gpsfiledepot.com/tutorials/how-to-load-maps-on-my-garmin-gps-unit/#pcbasecamp