If you are mapping as a professional then you need a very expensive GPS unit, but sometimes it is handy to have a just a regular consumer grade gps around. I have worked with numerous consumer gps units and have found that the one i find the most useful is a Garmin GPSMAP 60CSx. Here are some of the basic goodies:
- High-sensitivity GPS receiver that gets better reception under canopy and in deep canyons
- Barometric altimeter provides improved elevation data
- Electronic compass allows you to find a bearing while you are standing still
- IPX7 waterproof case lets you work in the rain and drop it in a puddle
- Large, color TFT display for easy day and night viewing
- Built-in Americas autoroute basemap, which gives you the basic layout of the major roads in the area
- Built-In Waypoint averaging, which allows you to get a more accurate waypoint position
- Good Battery life and field replaceable, AA batteries.
- Ability to add an external antenna
These last three benefits are what i consider making this a very useful mapping gps. The ability to add a external antenna is very useful while driving, or for stashing you gps in your pack and still being able to track. This is great when used in conjuction with a digital camera, and being able to geotag the images. The waypoint averaging allows you to increase the positional accruacy by averaging thelocation instead of taking a one time reading as the waypoint location.