Development of a technique to decompose heterogeneous mapping units in a categorical map of the biotic environment using correlated categorical data

In this article a technique is presented to estimate the proportions of dif ferent map categories in a series of heterogeneous mapping units, using inf ormation on the degree of spatial correlation with other categorical data. The technique has been applied to decompose ecotope complexes in a categori cal map of the biotic environment in Flanders, using secondary information on land cover and soil type. Because the conditional probability of an ecot ope occurring given a certain soil type depends on the frequency with which the ecotope occurs in an area, determining the probability of occurrence o f an ecotope from the conditional probabilities can lead to predictions tha t contradict prior knowledge about the composition of the different mapping units. A measure expressing the affinity of an ecotope for a soil type is proposed and is used as an alternative to conditional probability in the es timation procedure. The proposed method has been tested in a study area for which detailed field observations were collected, and proves to work well if reliable a priori knowledge about the composition of complex mapping uni ts is available.