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AI-GEOSTATS: Shared edges and cover types adjacencies/associations

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  • Santiago Saura Martínez de Toda
    Dear list members, I have calculated the shared edges existing between each of the cover types (nine in this particular case) of a vector map. My objective is
    Message 1 of 2 , Jul 29, 2002
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      Dear list members,
      I have calculated the shared edges existing between each of the cover types
      (nine in this particular case) of a vector map.
      My objective is to determine, on the basis of this shared-edge analysis,
      which cover types tend to be associated (adjacent/contiguous/next)to each
      other.
      A simple table with the length of the shared edges for each two cover types
      is not too meaningful. For example, one of the cover types occupies about
      70% of total landscape area, and thus the other cover types tend to share
      most of their edges with this dominant type. This (total edge shared) does
      not imply that there is a significant association (tendency for being
      located adjacent in the landscape). I tried to obtain a simple association
      measure that considered (corrected for) the effect of the different
      abundance of each of the cover types, but I don't feel really confident with
      the results I got.
      I wonder if there is available any association index or statistical test
      that determines whether a positive, negative or non-significant association
      exists between two given cover types in the landscape (preferably as derived
      from shared edges information). I guess this may be simpler to answer in
      raster than in vector spatial data.
      Thanks and best regards,
      Santiago Saura


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    • Roger Bivand
      ... Maybe a join count test, perhaps using the shared boundary length in the weights matrix - Cliff, A. D., Ord, J. K. 1981 Spatial processes, Pion, p. 20.
      Message 2 of 2 , Jul 30, 2002
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        On Tue, 30 Jul 2002, Santiago Saura Martínez de Toda wrote:

        > Dear list members,
        > I have calculated the shared edges existing between each of the
        > cover types (nine in this particular case) of a vector map.
        > My objective is to determine, on the basis of this shared-edge analysis,
        > which cover types tend to be associated (adjacent/contiguous/next)to each
        > other.
        > A simple table with the length of the shared edges for each two
        > cover types is not too meaningful. For example, one of the cover types
        > occupies about 70% of total landscape area, and thus the other cover
        > types tend to share most of their edges with this dominant type. This
        > (total edge shared) does not imply that there is a significant
        > association (tendency for being located adjacent in the landscape). I
        > tried to obtain a simple association measure that considered (corrected
        > for) the effect of the different abundance of each of the cover types,
        > but I don't feel really confident with the results I got.
        > I wonder if there is available any association index or statistical test
        > that determines whether a positive, negative or non-significant association
        > exists between two given cover types in the landscape (preferably as derived
        > from shared edges information). I guess this may be simpler to answer in
        > raster than in vector spatial data.

        Maybe a join count test, perhaps using the shared boundary length in the
        weights matrix - Cliff, A. D., Ord, J. K. 1981 Spatial processes, Pion, p.
        20. There is a version of the same colours (BB) test for R
        (www.r-project.org) in the contributed package "spdep", and SpaceStat
        (www.spacestat.com) also does it.

        Roger

        --
        Roger Bivand
        Economic Geography Section, Department of Economics, Norwegian School of
        Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
        Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93
        e-mail: Roger.Bivand@...
        and: Department of Geography and Regional Development, University of
        Gdansk, al. Mar. J. Pilsudskiego 46, PL-81 378 Gdynia, Poland.


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