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Re: GEOSTATS: sampling in ArcView

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  • Patrick van Laake
    Hi Steve, As far as I know, you can not easily construct a grid in ArcView. However, since you have a *real* GIS at your disposal I suggest you look up the
    Message 1 of 2 , Sep 14, 2000
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      Hi Steve,

      As far as I know, you can not easily construct a grid in ArcView. However, since you
      have a *real* GIS at your disposal I suggest you look up the GENERATE command in
      ArcInfo and have it generate a FISHNET for you, with your desired resolution and
      origin (so look up the extent of your other coverages first). BUILD the result and
      you have a valid polygon coverage that you could use in ArcView. But why not stick
      with ArcInfo? You probably want to take the label points from that coverage and turn
      that into a point coverage, INTERSECT that with all your polygon coverages and draw
      your selection directly from the resulting point coverage. Code snippet:
      >>>>>>
      generate <fishnet>
      fishnet
      ....

      build <fishnet>

      arcedit
      edit <fishnet>
      ef label
      sel all
      put <pointcov>
      quit

      intersect <pointcov> <your poly data> <pointsout> point
      <<<<<<<<< repeat this step for every poly data you wish to join to the sample
      points, using the <pointsout>
      as the <pointcov> in every successive run

      <<<<<<< End of snippet

      The final point coverage has all the attributes of all your poly coverages you wish
      to use in your analysis. Now, apply a nice scheme to draw from these points and
      you're home. If you wish to stratify the selection, just use one of the items from
      your poly coverage(s) that are now linked to the final points coverage.

      Good luck,
      Patrick van Laake

      Steve Bousquin wrote:

      > Can anyone suggest a procedure for randomly sampling an area in ArcView for
      > location of quadrats (sample units of a set area)?
      >
      > My intitial reaction (although I do not know how to do it) is to somehow lay a
      > grid of blocks of a specified size over the area (or a set of points a specified
      > distance apart), get the grid intersection or point coordinates into a table,
      > and sample randomly from this table, which will give me a list of selected
      > points, each of which will represent a location for placement of the corner of a
      > quadrat when field sampling (the distance between points will be the length of
      > the side of a quadrat).
      >
      > A neat solution would additionally let me lay the grid on and sample points only
      > within specified polygons, because the sample will be stratified by certain
      > polygon attributes (i.e., there will be different random samples from different
      > subsets of polygons).
      >
      > I have ArcInfo coverages for the area in question, which I view and manipulate
      > in ArcInfo. I am not a GIS technician.
      >
      > Thanks!
      >
      > Steve

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