I've used a GPS for 6 or 7 years doing cave locating and surveying. We locate the entrance with the GPS. After we have done the in-cave survey, it gets entered into a cave mapping software. This software will then convert all survey stations into UTM or lat-long coordinates. These coordinates can then be used to locate the cave passages while walking above ground. We also use the GPS to tell us whether we are on private property or state or federal. I can't imagine being without my GPS.
Do you know if there is a way to covert positions on a plat map into GPS coordinates?