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How To: Select island polygons

Summary

Island polygons are features completely surrounded by another feature or parent polygon.

Procedure

  1. Execute the COUNTVERTICES command with the POLY option.

    Code:
    Usage: COUNTVERTICES <cover> <LINE | POLY>
    Arc: countvertices testcov poly
    Counting vertices/arcs/islands and adding count to testcov.PAT


    Note:
    COUNTVERTICES adds three items to the polygon attribute table - VERTICES, ARCS and ISLANDS. ISLANDS will be populated with the number of island polygons contained within each parent polygon.


  2. In ArcPlot, select all parent polygons other than the universal polygon.

    Code:
    Usage: RESELECT <cover> <feature_class> {logical_expression}

    Arcplot: reselect testcov poly area > 0 and islands > 0
    TESTCOV polys : 2 of 9 selected.

  3. Create a selection file of the currently selected features.

    Code:
    Usage: WRITESELECT <selection_file> {<cover> <feature_class>}
    Arcplot: writeselect parent.sel

  4. In Arc create a new coverage containing only the parent polygons.

    Code:
    Usage: RESELECT <in_cover> <out_cover> {in_feature_class}
    {selection_file}{out_feature_class}

    Arc: reselect testcov parentcov polygon parent.sel

  5. In ArcPlot select the polygons from the original coverage that overlap
    the polygons in the new coverage.

    Code:
    Usage: RESELECT <cover> <feature_class> OVERLAP <overlap_cover>
    <overlap_feature> {selection_distance}{PASSTHRU | WITHIN}

    Arcplot: reselect testcov polygon overlap parentcov polygon # within
    TESTCOV polys : 5 of 9 selected.

  6. Select the island polygons.

    Code:
    Arcplot: reselect testcov polygon islands = 0


    You can draw the selected features now or repeat steps 3 and 4 to create
    a coverage that contains only island polygons.

    Note:
    Island polygons surrounded by the universal polygon will not be included in the final selected set.