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GEOSTATS: sampling in ArcView

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  • Steve Bousquin
    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
    Message 1 of 2 , Sep 13, 2000
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      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

      =======================================
      Stephen G. Bousquin

      Kissimmee Division
      South Florida Water Management District
      West Palm Beach, FL

      sbousqu@...
      =======================================


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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 2 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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