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675Re: AI-GEOSTATS: Shared edges and cover types adjacencies/associations

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  • Roger Bivand
    Jul 30, 2002
      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 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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