In GIS, to clip is to overlay a polygon on one or more target features (layers) and extract from the target feature (or features) only the target feature data that lies within the area outlined by the clip polygon. In other words, the boundaries of the second polygon are imposed on the first polygon. All other area is discarded and is no longer part of the first polygon feature The clipped data becomes a new feature. This is analagous to a 'cookie cutter' being used to cut a specific area out of a map to create a new, smaller map.
Clipping to form a new feature class creates a study area or specific area of interest that is an important function when working in GIS. This becomes advantageous when an analyst only needs to work with a certain focus area; he/she can discard the unnecessary spatial information with no loss to his/her core data. An example of using the clip tool would be analyzing traffic patterns at a college campus. An analyst does not need road data outside of the college campus, so he/she may clip the road data to the college campus boundary. A clip operation can be done using raster or vector data.
In Figure 1, the process of clipping a smaller area from a larger area is shown. The first frame depicts the original image, followed by the same image with the area to be clipped selected by the circle. Finally, the last image shows the new layer, clipped from the original.
- Dale, P. (2005). Introduction to mathematical techniques used in GIS. Boca Raton: CRC Press.
- ArcGIS 10 Help: Clip (Analysis). ESRI. Accessed 4 September 2012