accuracy of location of contacts and other features

Tue Apr 25 13:17:04 2000

A comment by Diane E. Lane about

SLTT Generic Conceptual Issues

by Tom Berg

Regarding Tom Berg's item J.:  The USGS, specifically the
 National Mapping Division, has defined accuracy standards
 for such lines as contacts.  A contact is
 to be shown as a solid line if it is located within a 
distance represented by 1 mm at the scale of the map. If not, 
it is dashed and defined as approximately located or dashed and defined
as inferred (no data to establish contact but contact must
be present), indefinite (insufficient data to establish
contact with certainty), or gradational (continuous change
from one lithology or rock type to another, contact arbitrary).
Concealed contacts are shown as dotted lines.  The same accuracy
standard applies to such features as folds and faults. For a scalable
database it would seem necessary
to state the accuracy explicitly at a given scale.
In actual practice, I (as a map editor) don't see many maps where the
author has tried to distinguish between approximate and
inferred contacts.   Even then, exactly what that means to the author
is not necessarily stated in the map explanation.

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