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Metoda wygładzania kartogramu jako alternatywa dla tradycyjnych sposobów wykonywania map izopletowych

Cebrykow P.

Polski Przegląd Kartograficzny

2005

T. 37, nr 1

3-12

W artykule opisano propozycję nowego sposobu opracowywania map izopletowych. Metoda oparta jest na kryterium zachowania zgodności mapy z wyjściowymi danymi statystycznymi i pozbawiona niektórych wad dotychczasowych sposobów sporządzania map izopletowych. Autor przedstawia również ocenę metody na przykładzie wykonanych map.

In order to prepare an isopleth map by smoothing of a choropleth one has to transform a discontinuous statistical surface into a smoothed version, preserving the volumetric properties of presented phenomena. The starting point is an unclassed choropleth map. Smoothing of the stepped choropleth surface can be described as a process of gradual cutting and smoothing of all edges on boundaries of space units. The method consists of four stages (fig. 2). In the first the appropriate database is prepared. In the second the statistical surface of phenomena is smoothed. In the third stage the course of isopleths is interpolated. The last, fourth stage covers graphical preparation. The map of forests in Poland is an example of such procedure (fig. 3). The new method of isopleth map preparation has been verified. A number of maps of population density in Poland were prepared basing on data referring to gminy (local administration units). Best results were obtained when the smoothing process was repeated using filters with gradually increasing size of the smoothing matrix (fig. 8). The results were also positive with iteration smoothing, using a small matrix of a small filter (3x3), but the representation of phenomena was too detailed, (fig. 7). Single smoothing with a large size matrix brought clearly negative results (fig. 6). The research concluded the following: - the method of choropleth smoothing is a proposal for a well ordered and methodologically plausible method of isopleth map preparation; - screen representation of data makes it possible for the shape and area of basic fields to influence the isopleth map, reducing the negative impact of their irregularities; - as a result of statistic fidelity of this method isopleth maps become a credible source of information; - the method makes it possible to obtain severalrepresentations of the same phenomenon, differently generalized from the same set of data. In author's opinion the suggested method deserves to be well received among cartographers. Its merits ought to encourage mapmakers to choose the medium of isopleth map more often as well as provoke more research on the method's further development.

Z problematyki określenia dokładności map izopletowych

Cebrykow P.

Polski Przegląd Kartograficzny

2004

T. 36, nr 4

259-265

W artykule opisano problemy związane z badaniem dokładności map izopletowych oraz przedstawiono źródła błędów na takich mapach.

The isopleth method is rarely used as a presentation method in cartography. There are several reasons for that. One of the main causes is cartographers' distrust towards isopleths, which bases on opinions of many cartographic authorities (Eckert, Imhof, Salishchev). The main dilemma is whether it is possible to represent discontinuous phenomena with isolines. The fact that this method is highly labor-consuming also limited its popularity. Furthermore, there are no clear, acknowledged criteria for preparation of isopleth maps. In order to establish how isopleth maps should be prepared one has to determine a universal tool for their evaluation. Volumetric criterion proposed by J.Moscibroda (1999) seems to be the optimal solution. In short, it preserves unity of a statistic volume of an isopleth map with the volume of continuous choropleth. Application of a criterion of behavior of phenomenon's statistical volume helps to trace down the sources of errors, which appear on traditional isopleth maps. The research made it possible to determine three basic factors which cause errors to appear. They are: the type of basic space units, location and number of reference points and the method of interpolation. Knowing the origin of errors and being able to evaluate them on isopleth maps provides a basis for research on how to improve the methods of their elaboration.