Geocoding Localities

Melissa C. Winans mcwinans at MAIL.UTEXAS.EDU
Tue May 21 12:24:00 CDT 1996


At 12:02 PM 5/20/96 EDT, you wrote:
>I am working on a geocoding project at USNM. We are in the process of
>working up protocols for enhancing specimen locality data by attaching
>latitude and longitude. The goal is to be able to use these data in GIS
>applications to look at everything from change over time to species
>distribution. I'm looking for feedback from other collections that may
>have done this or thought about it and other members of the community
>that may have thoughts and ideas. One of my concerns is augmenting
>imprecise localities with very precise lat/longs. We want this data to
>be meaningful and mappable but we do not want to imply more precision
>than we really have. Please email me with your comments at
>cvanhils at sivm.si.edu.

I agree with you that the precision of your data is a serious issue, and
that it is important to do something to inform the user of differences in
precision from site to site.  We had to deal with the same question when we
set up a GIS for our fossil specimen sites about 4 years ago; some sites
(especially the ones from the late 1800's and early 1900's) could not be
spotted precisely due to inadequate data, and others covered a large enough
area that it was not possible to represent them with a single point at the
1:24,000 map resolution we were using.  We solved this by doing three
things:  1) We marked sites that were too large to represent as a single
point with polygons outlining the extent of the site; 2) for sites where the
location was uncertain, but an educated guess could be made, we outlined the
most probable area and digitized that as a polygon; 3) we attached an
attribute to each point or polygon indicating the degree of reliability of
the plotting on a 5-step scale ranging from "Exact" at the top to "Wild
guess" at the bottom.

This still leaves you with the question of what to do about coordinates for
the sites that can't be represented as points.  Depending on how you do your
distribution analyses, you still may have to represent the large or
uncertain sites by a single coordinate pair (probably the centroid of the
polygon), but if your GIS attribute tables have a reliability attribute you
at least will be able to take whatever steps seem to be called for to
indicate the degree of certainty of each location.
****************************************************************
Melissa C. Winans, Collection Manager (mcwinans at mail.utexas.edu)
Vertebrate Paleontology Laboratory      Phone: 512-471-6087
J.J. Pickle Research Campus               Fax: 512-471-5973
University of Texas, Austin, TX 78712




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