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Rodzaje generalizacji treści map topograficznych na przykladzie mapy 1:50 000

Ostrowski W.

Polski Przegląd Kartograficzny

2003

T. 35, nr 4

251-258

Autor wyróżnia i bliżej charakteryzuje pięć rodzajów generalizacji kartograficznej, jakie zastosowano przy opracowaniu mapy topograficznej 1:50 000 na podstawie mapy 1:10 000.

The article presents an analysis of a process of generalization in the preparation of topographic maps. The analysis was conducted on an exaple of a Polish topographic map in 1: 50 000 published by Survey- or General of Poland in the years 1995-2002. Most sheets were obtained through the generalization of a topographic map in 1:10 000. Generalization of a 1:10 000 map into 1:50 000 is very evident ( the area is reduced 25 times). A comparison of the contents of these two maps makes it possible to determine how topographic maps are generalized in practice. The analysis points out that there are five basic generalization types used for generalization of a medium-scale topographic map (1:50 000). They are as follows: * selection of categories for presented objects and their classification * selection of objects within each category * approximation or elimination of quantitative characteristics * replacement of area symbols with point or line symbols * simplifacation of objects' shapes After generalization the number of contents' categories on a 1:50 000 map is 15% lower than on a 1:10 000 map. It results from various generalization processes: complete elimination of several categories, generalization of qualitative features of contents, combining meaning of several symbols, substitution of separate symbols with a joint symbol, introduction of new symbols representing general issues absent from maps in larger scales. Object selection is conducted with quantitative criteria (area, length, width, depth or height, density), qualitative criteria (spatial interrelations, functional criterion, name criterion) or mixed criteria (joint criteria). Quantitative criteria on a topographic map are generalized through reduction of the number of contour lines and lower accuracy of numeric description of object and points (e.g. height points, numbers of residents). On a 1:50 000 map signatures of relief altitude are removed. Area symbols representing dimensions of particular objects are replaced with point or line symbols. These dimensions can include the area, length or width of the object. Simplification of objects' shapes relies on the elimination of minute contour details and "holes" within a marked area, joining of neighboring area and occasionally enlarging small areas and widening of thin ones. The listed types of generalization basucally represent the consecutive stages of the process. First we select object classes, then objects within a class. Next we choose a presentation method appropriate for the size of the object in scale or with symbols; objects shown with area symbols are often simplified. Description of methods and criteria of generalization of topographic maps is vital for the attempts to automate the process.