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aggregation — English
A rather generalised description of the spatial distribution of a certain variable in a specific area. In their quest to describe the spatial distribution of a variable, geographers draw a map of the study area and indicate the entire area or areas where the variable might occur in that specific study area. It is like using a sieve with very large holes to sort the larger and smaller grains of a heap of rock debris (see “weathering” and “mass wasting”). All the particles larger than sand size are separated from the debris mass, but we know that in the remaining heap of material, grain size is still highly variable. In a graphic representation we can draw a generalised map of the spatial distribution of, say, affluence in a city. First, we group together all the houses that are worth more than R1 million. The areas where these houses occur are demarcated on a map. We might find a small number of such areas (say, three or four). This way we have produced a map of the distribution of wealth in the city. But we know that some of the houses in those demarcated areas are worth R10 million, others R5 million and some only R1 or R2 million and some are not even worth R1 million. We have actually aggregated data, that is, grouped together all expensive houses in the city to obtain a generalised picture of spatial distribution of wealth. Should we want to do a finer analysis, we shall have to disaggregate the “wealthy” areas in the city, by further sorting. Then we use a stricter set of criteria (like a set of finer sieves) and distinguish those houses that cost more than R10 million from those that cost between R8 million and R9,9 million, and so forth. The original three or four identified areas will fall apart and form a larger number of smaller areas. In this way we draw a far more detailed map and our representation of the spatial distribution of affluence is far more informative than the map drawn from the aggregated data. Exactly the same technique is used for all types of spatial data, for instance the distribution of vegetation types, the occurrence of sinkholes, the distribution of wetlands, the distribution of foreigners in a country, and so forth. (See “disaggregation”.)
