Arc4You Poly Clean

With this extension for ArcView 3.x you can clean the topology of polygon themes. All possible errors like destroyed or overlapping polygons as well as gaps between the polygons can be cleaned. You should clean a polygon theme after importing (e.g. from ARC/INFO Coverage or AutoCAD drawing) as well as after editing or geoprocessing it (e.g. intersecting polygon themes using GeoProcessing Wizard or XTools). Particularly before final data transfer or conversion into a ARC/INFO Coverage this cleaning should happen.

Why is the topology of polygon shapefiles often incorrect?
Why shall I truncate the coordinates of all vertices?

When you load the extension into your ArcView project, the new button will appear in the button bar.
Click on this button to analyze and clean the active polygon theme.

Hint: Press the Shift key when clicking on the button in order to reopen the command with the previous settings. Thereby you can repeat the cleaning process or apply the same cleaning on other themes.

What's new in version

What's new in version

With this extension the following errors can be found and cleaned automatically:

How to find fuzzy vertices: In a shapefile each vertex between adjacent polygons should exist twice, each corner point between several polygons (node) three or multiple times and each vertex along the outer border once. You can get the marginal vertices by combining all polygons to an overall polygon. All other single vertices are fuzzy.

How to find thin polygons: To identify thin areas (so-called Sliver Polygons) we use the so-called Thinness Ratio, the relation between the area of the polygon and the square of it's maximum elongation in X and Y axis (e.g. 100x100 m at an X/Y extent of 30/100 m). This value is reciprocal to the QDRatio or Thickness Ratio (that is for example used in the extension Edit Tools of Ianko Tchoukanski). The larger the value, the thinner is the polygon. At a value of 10 the polygon covers the tenth part of its extent. Squares reach the minimum value of 1. In opposite to the Sliver Ratio (area-perimeter ratio - introduced in ArcView 3.2) this value is independent from the length and frayness of the polygon contour. Even a dense network of finest "veinlets" would not be classified as thin (i.e. would achieve a small thinness ratio), if it fills a major part of its extent.

How to find gaps and overlaps: The algorithm for the detection of gaps and overlaps has been optimized in speed (as far as this is possible in Avenue) and requires only a few minutes even for thousands of polygons (the duration increases linear by the number of polygons). This is achieved by dividing the theme in rectangular areas of some hundreds of polygons and analyzing each area for gaps and overlaps at a single step. If one of these areas contains more than 400 polygons, it will be divided in equally sized rectangles with approximately 200 polygons each (e.g. an area with 800 polygons will be divided in 2x2 rectangles). If you have activate the option Display Errors as Graphics, the currently analyzed area will be drawn as a black frame.

2003 WLM Klosterhuber & Partner OEG