In the pre-gps era, I calculated the area of one of my study sites using a high resolution USGS map. Recently we checked that value using a GPS. For the part of the study site that is fairly flat, the numbers match up very well. However, for the part that has a significant downhill slope, they do not. The difference is striking - the gps-derived value is nearly 40% smaller than the USGS map-derived value. The gps values were differentially corrected and done with a Trimble that should be accurate enough that I would not expect a difference of over a hectare between the map and gps area values.
Does anyone have any experience or advice for dealing with area calculations in areas of ~3-5 ha, involving significantly uneven ground? thanks, Carol Carol Boggs Dept. of Biology Stanford University summer: Rocky Mtn. Bio. Lab Crested Butte, CO
