Reply to "Elevations above Sea Level"

tomriegelMember

City or County topo is becoming widely available in the U.S. Some Government websites offer it in a variety of formats, including AutoCAD. A proper road profile is time-consuming to generate, but with a little software and time, it is easily done.
The accuracy of ALL topographic information is assumed to be within one contour interval, meaning if the USGS says it's 1320 with a contour interval of 20', it means it's in the rage of 1310 to 1330. Since USGS started mapping, several datums have been used, and they vary from state-to-state.
I believe the way Topo USA generates the surface is an over-simplified model using only the point data on USGS, the contours are an image. I have encountered much larger errors than these in my experience.

1/20/0511:34 AM

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