What is Snapping in GIS?

Snapping in GIS occurs during the editing of a GIS dataset.  Snapping involves connecting a geometric vertex or edges of one feature to another.  Snapping is an important setting when editing or creating GIS data because it ensures that edges and vertices that need to be adjoining are cleanly connected.  Without snapping, errors in the data such as overlapping polygons, spaces between polygons, and overlapping lines can occur.

The polygon on the left was created without snapping, leading to overlapping features.  With snapping, the polygon on the right was created to align with the adjacent polygons.

The polygon on the left was created without snapping, leading to overlapping features. With snapping, the polygon on the right was created to align with the adjacent polygons.

Setting up snapping in GIS involves setting a few parameters.

First, decide if vertices (or nodes), edges (or segments), or both need to be snapped.  Next, the snapping tolerance needs to be set.  This determines the distance away a vertex or segment needs to be to a neighboring feature in order to snap it.  Setting this tolerance becomes important because you don’t want to accidentally snap features together that weren’t mean to be together because the snap tolerance was set to high. Conversely, a snap tolerance set too low runs the risk of not snapping features together that you need snapped.

Setting a proper snap tolerance ensures that spatially close features are snapped together.

Setting a proper snap tolerance ensures that spatially close features are snapped together.

How to Set up Snap Tolerance and Snap Options

Instructions on how to set up snap options while editing GIS data are specific to each GIS software.  Directions can usually be found in the documentation section on editing.  Here are a few quick links to the more common GIS software programs:

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