1. Classification, retrieval, and measurement functions. All functions in this category are performed on a single (vector or raster) data layer, often using the associated attribute data. Classification allows the assignment of features to a class on the basis of attribute values or attribute ranges (definition of data patterns). On the basis of reflectance characteristics found in a raster, pixels may be classified as representing different crops, such as potato and maize. Retrieval functions allow the selective search of data. We might thus retrieve all agricultural fields where potato is grown. Generalization is a function that joins different classes of objects with common characteristics to a higher level (generalized) class.1 For ex- ample, we might generalize fields where potato or maize, and possi-bly other crops, are grown as ‘food produce fields’. Measurement functions allow the calculation of distances, lengths, or areas.More detail can be found in Section 6.2.
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