GIS, label data, and fuzziness scale

Eric Metzler metzler at NRULT1.DNR.OHIO.GOV
Tue Aug 23 12:10:10 CDT 1994


Three recent postings spell out the need for accurately transcribing
data from historical specimens to databases that need exactness
while not foolishly creating precision.  As previously stated, the
data for most species are unaffected by creating precision, but it
may be irresponsible to add precision for many data, thus a way to
transcribe data is needed.

The Ohio Lepidopterists society conducted a six year
Comprehensive Survey of Moths and Butterflies in Ohio for the
Ohio Department of Natural Resources, Division of Wildlife.
During the survey, which ran from 1986 through 1992, The Ohio
Lepidopterists accumulated nearly 100,000 individual records of
butterflies and moths in Ohio.  Label data disclosed over 2,400
discrete collecting sites.  It was necessary to convert these data to
latitude and longitude without creating precision.  At the
suggestion of Dr. Daniel Otte, the Academy of Natural Sciences
in Philadelphia, PA, USA, The Ohio Lepidopterists developed a
fuzziness scale that preserved the original data in a lat x long
format.  Our fuzziness scale was devised to take advantage of the
labelling habits of most Lepidopterists.

GIS pixels can be programmed to accommodate any size area for a given
datum, thus the fuzziness scale in concert with the provided lat x long
data will not create precision when data are stored.  In other words, a
lat x long datum with a fuzziness scale of S6 will produce a location the
size of 36 square miles.  Such a fuzziness scale should be applicable to
any organism, including marine organisms.  The scale may have to be
tailored to the situation at hand, but the principle is the same.

The following is taken from the report submitted by The Ohio Lepidopterists to
the ODNR Division of Wildlife.  For more information, you may contact: The
Ohio Lepidopterists, 1241 Kildale Sq. N., Columbus, Ohio  43229-1306.

          THE COMPREHENSIVE SURVEY OF OHIO
                MOTHS AND BUTTERFLIES
        completed by The Ohio Lepidopterists
               Project No. NGSCW-91-11

  Information pertinent to the concept of RELATIVE
                      CERTAINTY
             in the final report to ODNR
                  30 September 1992


The Ohio Lepidopterists strived to provide detail about the capture
localities of the records in the collective databases.  The detail included
all information from the locality labels associated with each specimen.
In addition, The Ohio Lepidopterists sought to provide the latitudinal and
longitudinal coordinates for as many of the collecting localities as
possible.  The purpose of this report is to provide information pertinent
the methods used to calculate those coordinates.

Two thousand one hundred fourteen discrete collecting locations were
registered for specimens collected in Ohio.  The exactness of the
localities varied from vague, such as someplace within the state of Ohio,
to extremely specific, whereby the stated location is q a few feet.  The
center of each location was used to record the latitude and longitude, but
given the unequal size of the recorded locations, a method was developed
to stipulate the size of the geographical area represented by each locality.

A SCALE OF RELATIVE CERTAINTY was conceived to represented
the size of the area for each locality. The Scale of Relative Certainty was
designed to reflect the precision of the data labels.  Since some labels
indicate a linear site, i.e. "along highway 82", the Scale of Relative
Certainty has two scales, one for square area, S1, S2, etc., and one for
linear sites, L1, L2, etc.  The Scale of Relative Certainty is printed at
the end of the report.

The method of plotting Latitude and Longitude is straight forward.  If
the collector knew the latitude and longitude, those calculations were
used.  For most other sites, county maps as published by the Ohio
Department of Transportation (ODOT) were used.  Occassionally the
ODOT maps were supplanted by 7.5' topographic maps, other county
maps, or other city maps.

The ODOT county maps included tick marks for latitude and longitude.
In a few cases, i.e. Lake County and Ottawa County, the tick marks
were found to be in error, thus The Ohio Lepidopterists used topographic
maps to replace the ODOT tick marks with correct coordinates.

The locations written on the specimen data/locality labels were located
on the county maps, and a rule was used to calculate the latitude and
longitude to degrees, minutes, and tenths of minutes.  For locations that
indicated an area, i.e. Vinton County, Brown Township, Section 11, the
center of the area was used as the precise spot for the latitude and
longitude.  For linear sites, the exact center of the linear site was used
to calculate the latitude and longitude.  The Scale of Relative Certainty
was employed to determine the correct uncertainty code.

The uncertainty codes were applied starting from largest area to smallest
area.  Localities were not made to fit into the most precise code.  For
example, the square area of the City of Columbus is larger than a
township but smaller than a county.  Rather than make the square area
of the City of Columbus more precise than stated on the label, the code
for county, S7, was used.  Given the diversity of habitats in an area the
size of Columbus, accuracy greater than what is stated on the data label
creates precision that is unwarranted.  As the sizes of the localities get
larger, useful detail about the habitat requirements of the species are lost.
Future researchers can use the database to access the specimen if they
need to know more about the sample.

The codes of relative certainty were recorded in the database in degrees,
minutes, and tenths of minutes.  The computer used these data to
calculate the coordinates in degrees, tenths, hundredths, and thousandths
of degrees.

The Scale of Relative Certainty follows:



             SCALE OF RELATIVE CERTAINTY
                 September 28, 1992

CODE DEFINITION

S1        Precise location, plus or minus 200 ', is known.
S2        Location is known to be within a circle 1/4 mile in
          diameter.
S3        Location is known to be within a circle 1/2 mile in
          diameter.
S4        Location is known to be within a Section or
          equivalent.
S5        Location is known to be within a circle 2 miles in
          diameter.
S6        Location is known within one township (about 36
          sq. miles) or equivalent.
S7        Location is known to be within a County.
S8        Location is known to be within 1/2 of the State of
          Ohio.
S9        Location is known to be within the State of Ohio.

L1        The linear site is known to be no more than 1/2
          mile long.
L2        The linear site is known to be no more than 1 mile
          long.
L3        The linear site is known to be no more than 2 miles
          long.
L4        The linear site is known to be no more than 6 miles
          long.
L5        The linear site is known to be no more than 36
          miles long.
L6        The linear site does not exceed a distance equal to
          1/2 of the State of Ohio.
L7        The linear site does not exceed a distance equal to
          the diameter of the State of Ohio.


Eric H. Metzler
Ohio Department of Natural Resources
Columbus  Ohio  43224
metzler at nrult1.dnr.ohio.gov
(614) 265-6774




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