Working with raster data

Raster data, stored in GRASS as a matrix of values, represent either a continuous field (surface), an image, or geometric objects (points, lines, areas) corresponding to discrete fields (Figure 5.1). For surfaces, the values in the matrix are assigned to the center points of grid cells. They represent the actual measured or computed values (e.g. elevation, slope, temperature). For noncontinuous fields (images, geometric objects), the values are assigned to the entire cell area and represent the category number.