Generalize – ArcView 3.x Extension

By | February 3, 2009

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This Arcview extension provides a dialog-based tool to simplify the currently selected shapes in a polyline or polygon shapefile. This tool is used to generalize, or weed out, vertices that do not add to the desired level of detail in the geometry. A tolerance is specified to check whether or not vertices should be retained.
This script is a simple implementation of the Douglas – Peucker algorithm used in ARC/INFO and PC ARC/INFO. The dialog is initiated from a button in a View GUI.

  1. The extension does not make a new shapefile. It changes the currently active polyline or polygon shapefile. Changes can be Undone using the standard shape editing tools in Arcview.
  2. The extension will reduce the quality of the data. Any metadata for the themes should state that the data are modified.
  3. The extension will generalize all the selected polylines or polygons.
  4. Results are very dependent on the polyline or polygon geometry. While the shape endpoints are maintained, interior points may be eliminated. Other shapes in a network that may begin or end at an interior vertex may now be dangling. A complex shape may cross itself after being generalized. Neighboring polygons will no longer match edges. Proceed with caution.
  5. This script does not recalculate lengths or areas. They may have changed as the shapes are simplified. The View.CalculateFeatureGeometry (calcapl.ave) sample script can be used to update the values.

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