GeoBase - Geospatial Engine

Raster data type consists of rows and columns of cells where in each cell is stored a single value. Most often, raster data are images (raster images), but besides just color, the value recorded for each cell may be a discrete value, such as land use, a continuous value, such as rainfall, or a null value if no data is available. While a raster cell stores a single value, it can be extended by using raster bands to represent RGB (red, green, blue) colors, colormaps (a mapping between a thematic code and RGB value), or an extended attribute table with one row for each unique cell value. The resolution of the raster dataset is its cell width in ground units. For example, in a LIDAR raster image, each cell is a pixel that represents an area of 3 meters by 3 meters. Usually cells represent square areas of the ground, but other shapes can also be used.

 

Source: Wikipedia