Very rarely is an analyst interested in an entire satellite scene, which can easily cover hundreds of square miles. Given the size of satellite data, we are highly motivated to reduce the size of an image to only our area of interest. The best way to accomplish this reduction is to clip an image to a boundary that defines our study area. We can use shapefiles (or other vector data) as our boundary definition and basically get rid of all the data outside that boundary.
The following image contains our stretched.tif image with a county boundary file layered on top, visualized in Quantum GIS (QGIS):
To clip the image, we need ...
