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Horizontal_Positional_Accuracy_Report:
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Although a relatively low Root Mean Square (RMS) error was achieved in
registering the scanned images, When the coverage was digitized there remained
discrepencies with the ESRI sourced coverage. (ESRI Arcworld is chosen
as a standard because it is widely accepted and available.) These discrepencies
are in part the result of the registration problem, and in part caused
by compilation differences between UNESCO and ESRI. Using a roving window,
piecewise rubbersheeting was performed with the Arc/Info adjust command,
polygon option. Identifiable features of inland water bodies and shorelines
common to both sources are used as targets to create the "to - from" links
for adjusting the coverage. Overlaying plots of this coverage, corresponding
to the source maps in scale, projection and map extent, on a light table
shows a variable offset ranging from 0 to 1 mm (5 km).
The following describe the tolerances:
1. Original geologic maps are presumed to be of 500 meter maximum accuracy
(0.1mm at 1/5,000,000 scale)
2. Scanned images are of 200 dot/inch resolution
(0.13 mm on paper map)
3. Scanned images were registered and rectified
with an average RMS error of ~600 meters. (0.06 mm on paper map)
4. Fuzzy
tolerance was set at 250 meters (0.31 pixel) and weed tolerance was set
at 250 meters (0.31 pixel)
5. 100 points were sampled on the master coverage
for fit with ESRI Arcworld country boundaries and an RMS error was calculated
of 1,437 meters, the maximum error was 5,045 meters.