Newsgroups: bit.listserv.ingrafx
Date:         Sun, 27 Dec 1992 19:30:43 EST
From:         Faustino Arao Daria <fad8t@AMAZON.EVSC.VIRGINIA.EDU>
Subject:      quantification of the data content of a map

This relates to a posting dated Dec 18, 1992 which invited comments
on a proposal :

==========================================================================

The Quantification of the Efficiency of Transmission of Cartographic Data.

             A proposal submitted for consideration in:
          Department of Geography, University of Portsmouth.

                              by

                          PAUL DARLOW,

             Undergraduate, Department of Geography,
                  University of Portsmouth.
                     (December, 1992)

==========================================================================


Comments :


One of the five aims of Paul's Proposed Research Project is the

     Construction of a methodology
     to enable the quantification of the data content of a map.

Paul has considered two approaches in his METHOLOLOGY
(text reformatted) :

          "The quantification of spatial relationships is
     substantially more difficult than quantifying map features.
     Two initial approaches are recognised at this moment in time,
     although experimentation with various concepts may produce
     a more satisfactory solution.

     The first approach is to make the assumption that the
     blank areas of a map are just as important as those areas
     containing feature data. It can be said that a feature
     not appearing in one location is of no less importance
     than that feature appearing in another location.
     If this assumption is made, all locations on a map have
     equal relationships with all other locations on that map.
     Quantification of relationships is then relatively simple,
     by calculating the area of the map, dividing by the area
     of the smallest 'bit' of information on the map and then
     relating the answer to the scale of the map.

     The second approach is to use a computerised analysis of the
     distance between each feature and every other feature on the map.
     If the computer is set-up to keep a total of the distances,
     eventually a final total can be produced, which could be used
     to quantify the geographical relationship."


Be it a raster-based or vector-based data, the information contained
in a map file can be sent to a POSTSCRIPT printer as a PS/EPS file.
Can the file size be used as an indication of the quantity of the
data content of a map ?

By way of analogy, suppose the size of the postscript file of a
"Where's Waldo" picture puzzle (vector-based) is

           1.1 Meg with    Waldo and
           1.0 Meg without Waldo.

Assume that the Waldo cartoon character accounts for the 0.1 Meg
difference.

    Can we conclude that the data content is higher in the
    postscript file which includes Waldo ?
    If yes, can we make the same inference in the case of a map ?



Consider the files in an ESRI graphics subdirectory.  Each file
contains information on a particular feature of interest.
The POSTSCRIPT command in ARC/INFO (v. 6.1) converts the files
in such a subdirectory to one postscript file.

If there are more features of interest to a mapmaker or GIS programmer,
then there will be more files in such a directory, and
consequently, the Postscript file will be larger.

    Can we consider a POSTSCRIPT printer to be a dispassionate,
    unbiased or objective map-percipient ?  If so, is there a need
    to conduct experiments to determine the characteristics of an
    'average' map-percipient ?
Comments: Gated by NETNEWS@AUVM.AMERICAN.EDU