Converting Township Range Section data to lat/lon
dyanega at POP.UCR.EDU
Mon Aug 21 19:41:59 CDT 2000
Mary Barkworth wrote:
>for many specimens
>collected in the U.S., the most accurate locality data on a herbarium
>label is the TRS data. It provides location within a mile.
Given that, how do you deal with the uncertainty involved when converting?
Do you give a list of the four lat/longs that define the corners of the
box, or do you list the lat/long of the exact center of the box? I can
imagine that giving the corners, while more useful in one respect, would
not be very good for exporting data into mapping programs. Are there
mapping programs that will happily map a locality as a box covering, say,
one full degree of lat/long, or are all mapping programs limited to single
points in space?
Perhaps more to the point, do we as a community have anything like a
consensus as to how precise a coordinate must be before we will consider it
*viable* for use in mapping? After all, if you have records as in my
example above, where only the nearest *degree* is available, then it's
theoretically possible for the actual collecting site to be something
around 40 miles away from the "centroid" (X'30", Y'30"). Is that kind of
error acceptable? If not, and people just go ahead and enter all records
into their databases and have them converted to single lat/long values, how
do users of such data sets know whether or not such unwelcome points are IN
a data set they may be accessing remotely, for example? Does every
collection-record database in existence actually have a "linear error +/-"
field in it? What's the cutoff, anyway? 10 miles? 5? 1?
Perpetually wrestling with this sort of thing,
Doug Yanega Dept. of Entomology Entomology Research Museum
Univ. of California - Riverside, Riverside, CA 92521
phone: (909) 787-4315 (standard disclaimer: opinions are mine, not UCR's)
"There are some enterprises in which a careful disorderliness
is the true method" - Herman Melville, Moby Dick, Chap. 82
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