Geographic raster files are similar to pixel image (bitmap) files in computer graphics. Their format is often that of an image data file (.tif, .ecw, .jpg, .png …), to which are added georeferencing information by an associated file through internal storage (GEOTIF format, for example). Files associated with multichannel remote sensing combine together several images. Raster files are often very large and are rarely compressed using standard methods since the associated geographical information risks being lost. Specialized compressed formats exist: .ecw, .sid. The display of raster files is often accelerated with a quadtree type of indexation, called “pyramid” in certain software.