By selecting a region representative of such classifiers, we can use the computer to classify all the rest of the pixels in the image as well. In color space, we take all the pixels from a selected, labelled area, such as one of the green rectangles at the left. If indeed this region represents a homogeneous land cover, then those pixels will be closely clustered in color space. We can take the average position of those pixels to represent that type of land cover. Proceeding in this way with all the selected regions, we can assign each land cover type to a point in color space.
Classification is done in order to make quantitative measurements of images.
If, for example, we believe that the quantity of salt-marsh is decreasing for some reason, then a set of images from different times gives a qualitative idea that is open to interpretation.