The most important characteristics of the satellites used, is their resolution and the spectral bands that they cover. The satellite's resolution is the minimum land area that can be represented with the smallest image unit, that is, the pixel. The Spot satellite, for example, having a pixel size of 10 by 10 meters in panchromatic mode, can represent a street 10 meters wide, or a building with 10 meters sides. The spectral bands covered vary for each satellite and do not concern the visible areas only. Fro example, the Landsat satellite can cover seven different bands, four of which are outside the visible range (infrared, thermal). | 
