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Subject: Contours and isolines
Date: Fri, 30 Sep 2005
From: Harry O. Davis <[log in to unmask]>
To: [log in to unmask]


I concur in the concern presented by Nancy Kandoian and the remarks offered
by Russell Guy concerning relief.

To limit one's conceptualization and use of the term "contour" to only
surface expressions of elevation above sea level is at odds with what is
found on some maps.  Although it might be argued that one should use only
"isoline" (or a cognate term such as "isopleth" or "isopach") and not
"contour" when identifying a sub-sea or subsurface situation, the reality
is that "contours" (with contour intervals) appear on many geologic and
geophysical maps, either as elevation or depth measurements and also as
expressions of other parameters (such as gravity intensity).  Additionally,
an argument can be made that isolines showing depth (inverse relief) are
negative contours, or, more correctly, contours with a negative value
relative to sea level.

To complicate matters further, note that the term "bathymetric contour" is
employed in the USGS 1:100,000-scale topographic-bathymetric series.   And
people do speak of the "relief of the ocean floor."

Then there is the need to distinguish between absolute relief (altitude)
and relative relief.

Looking at our collection here I find maps whose titles speak of "bedrock
surface," "contoured base [of a formation]", "structure on top of ...,"
"depth to bedrock," "subsurface contour map," etc., all using contours with
contour intervals.  Then there are other maps (such as those showing
thickness of glacial drift) that employ isopachs or other isolines.

The responses to Gwen's question still leave me uncertain as to when a
cataloger should code relief and when not to.  And if there are contours or
other isolines present on the map depicting other than surface
(topographic) relief, what is the appropriate coding?

Thanks for any additional insight into all this.

Harry Davis





Harry O. Davis
Map Librarian
Morris Library / MS 6632
605 Agriculture Drive
Southern Illinois University
Carbondale, Illinois 62901

Phone:  618-453-2372 or 618-453-2705  <> FAX:  618-453-2704
Internet: [log in to unmask]