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Dear Kathryn, Dan and Colleagues,

Dan is quite correct in saying there are no easy ways to measure a boundary
using maps and plans. The accuracy is dependent on the scale of the map,
the map projection, the geodetic model of the earth used, and the original
ground measurements that were used to produce the map in the first place.

The only way to obtain an accurate assessment of the length of a boundary
is to survey the boundary on the ground. Even with a ground survey the
accuracy of the result depends on the number of points located. Straight
(geodesic) lines are easiest to measure and compute. The resulting distance
is commonly called an ellipsoidal distance as the mathematical
representation of the earth is an oblate spheroid or ellipsoid of
revolution (the radius if the earth is approximately 22 kilometers longer
at the equator than the radius at the poles.)

Natural boundaries such as coastlines, mountain ridges, rivers (centers or
banks of rivers) are especially difficult to measure. The more points
located, the more precisely one can obtain the result.

The limiting factor in boundary measurement by survey is cost. The more
points required the greater the cost. Though with GPS available, the cost
nowadays is far cheaper than the measurement of angles and distances as was
done in the past.

This is not to distract you from your work with maps.  I just wanted to
point out the difference between the reliability of results obtained using
map records and those obtained by direct measurement.

Luck to you all,
Gary Jeffress


 Dr. Gary Jeffress, R.P.L.S.
 Professor of Geographic Information Science
 GIScience Program
 Department of Computing and Mathematical Sciences
 Texas A&M University-Corpus Christi
 6300 Ocean Drive
 Corpus Christi, Texas 78412
 Phone (361) 825-2720
 Fax (361) 825-5848
 EMail [log in to unmask]
 Room ST211
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