Over the past two years, there have been numerous questions on inputting a
paper map into mapinfo. Most answers indicated that if you had points with
known coordinates, digitizing was a convenient method of input. In the most
recent discussion, George Smith indicated that the more points with known
coordinates the better (intuitively this sounds correct).
I have found that just the opposite is true. I have had to input specific
data from numerous USGS quad maps. I discovered that if I entered more than 3
control points, the accuracy of the digitizer-to-mapinfo mapping was seriously
degraded (both in the numeric calculations and in comparing puck location with
the map on the screen). The more control points that were included, the
greater the location errors. The best accuracy always occurred with only 3
control points.
why?
S. Figuers
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