Many classes give the richness of detail that allows the minutest distinctions between the squares, whereas details are lost if the squares are grouped in a few large classes. A digital image is a chorological matrix. The size of the squares in the grid, the spatial resolution in the satellite image, depends upon the system providing the data. Similarly the number of classes is determined by the ability of the equipment to distinguish nuances. Digital images often hold a division into 256 classes, which is matched exactly by the capacity of 1 byte in the computer.
Every pixel is given a grey shading corresponding to the pixel value.
Now the matrix will appear on the screen as an image or a thematic map. For many years maps have been based on airal photography where the developed pictures could function as maps immediately. Each scanning area is given a number corresponding to the amount of radiation. As the geographical coordinates of each area are also known we have a chorological matrix. The map may thus be manipulated endlessly, maps may be superadded, subtracted, multiplied and divided.