Sliver polygon

In fact, in 1978 Michael Goodchild found that they constituted the majority of all polygons in some operational GIS.

[2] Early programs for performing vector overlay, such as WHIRLPOOL, developed mechanisms for preventing sliver polygons, such as the "epsilon filter" (fuzzy tolerance)[3] In recent decades, most of the focus of software vendors and practitioners has been on improving the quality of GIS data to prevent them.

Sliver polygons are typically created when polygons are automatically generated from lines that should be coincident (e.g., an international boundary following a river de jure, or two adjacent counties) but are not, due to the natural discrepancies that arise from manual or automated digitization.

During the overlay process, the preferred mode of sliver polygon prevention is the use of a fuzzy tolerance, which is sometimes called a "xy tolerance" (ArcGIS) or "snapping threshold" (GRASS), and was originally called an "epsilon filter.

The choice of a proper fuzzy tolerance depends on the situation, especially the scale of the data, and can be a challenge.