What are Weird Polygons?

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Weird polygons can happen during GIS data creation when nodes marking the perimeter of a polygon are digitized out of order in a way that creates an intersection of lines.  The straightforward definition of a weird polygon is a data feature that is missing nodes.  One way this happens is when the polygon is digitized in such a way that one arc cross another arc.  While the end feature looks like two polygons, the cross lines are not connected by a node.

A weird polygon is a digitized polygon that is missing a node where two lines cross.
A weird polygon is a digitized feature that is missing a node where two lines cross.

A second way weird polygons can happen is when a digitized line feature is cross over upon itself.  As with the first example, the resulting digitization error makes it appear as if the feature is a polygon but the intersecting lines are missing a node.

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About the author
Caitlin Dempsey
Caitlin Dempsey is the editor of Geography Realm and holds a master's degree in Geography from UCLA as well as a Master of Library and Information Science (MLIS) from SJSU.