INCLUSIONS: degree of purity of the map units
The purity of a map refers to the spatial variability of its components and the different soil properties outlined within a given map unit. Spatial variability depends on the scale of the map, the spatial location and the property in question.
It is important to remember that a map unit (which is apparently uniform due to the fact that it is represented in a certain way in all of its delineations) never implies complete homogeneity within the delimited area.
A degree of purity of a given map depends on whether it describes certain areas that cannot be faithfully represented at the chosen map scale (inclusions).
The significance of these impurities depends on whether they relate to similar or dissimilar soils (soils with a different response to the use in question compared to the predominant soil).
As the heterogeneity of the map units increases, the reliability and value of the map for making predictions decreases; hence the limited interest and use of small scale maps, such as those at a scales of 1:100 000 or less, for land management.
Series maps require at least 85 % uniformity, (in other words, less than 15% of the area occupied by inclusions). Nevertheless, in maps at the family hierarchy level, homogeneity decreases to 70 % and, in cases of very overlapping distribution models, it may even fall as low as 50 %.
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