Badania czytelności kartograficznych anamorfoz powierzchni

W artykule omówiono badania czytelności anamorfoz powierzchni oraz zarysowano problematykę tego zagadnienia. Prezentacje tego typu są pochodnymi kartodiagramów lub kartogramów (R. Szura 1989), dlatego właśnie z tymi formami prezentacji kartograficznej najczęściej porównywane są anamorfozy powierzchni. Ważną cechą omawianych map jest możliwość prezentacji danych absolutnych oraz łączenie anamorfoz z różnymi metodami prezentacji kartograficznej, głównie kartogramem i kartodiagramem. W artykule wskazano również, które zagadnienia związane z czytelnością tego typu prezentacji nie były dotychczas badane, a należałoby je lepiej poznać w celu usprawnienia przekazu informacji przestrzennych.

The article's aim is to clarify notions related to the problematic aspects of cartogram readability, especially those of value-by-area maps (area cartograms). The value-by-area map is a particular form of presenting data on a map, in which basic unit area is changed depending on phenomenon value. For example, if we present world population by country, the area of each country will be proportional to its population. Cartograms are elaborated and used more and more often in various publications, especially on the Internet. This is a result of the development of GIS programs, which accelerate cartogram generation. Since such presentations appear more and more often, one should think about their perception - what do they convey, whether they are appropriately interpreted and what is viewers' attitude towards them. The first research on cartographic readability was done by B. Dent (1975). The experiment consisted of three parts, which covered: assessment of phenomenon value in basic units through a singular field created in the legend; both the shape of basic units and the shape of range in the legend were important; comparisons of interpretation efficiency of cartograms and circle graduated diagram maps with Flannery's scaling; subjective cartogram evaluation, done by respondents on three levels: general reaction to a presented map, method of presentation on the map and map readability. Research shows that contiguous regular cartograms with preserved spatial continuity are interpreted most efficiently. It is necessary to apply a legend in the form of a square unit with a relatively small phenomenon value. The second test showed that the cartogram is equally efficiently interpreted as the circle graduated diagram map. According to recent research cartograms are an interesting and innovative but difficult to read method of conveying information. Other research pertaining to cartogram readability and interpretation was done by: T.L.C. Griffin in 1983 - identifying areas on cartograms, D.Z. Sui and J.B. Holt in 2008 - map evaluation by respondents, Hui Sun and Zhilin Li in 2008 - comparison of cartograms with traditional methods of cartographic presentation and the comparison of usefulness of various types of cartograms, I. Kaspar, S.l. Fabrikant and P. Freckmann in 2011 - comparison of cartogram and circle diagram map together with choropleth map readability. In the first experiment T.L.C. Griffin indicated that for a good orientation of areas presented on a cartogram, it is necessary to know the geographical position of these spatial units in relation to one another. D.Z. Sui's and J.B. Holfs research referred to the third part of B. Denfs experiment and showed that respondents answer better to cartograms, if they know the main assumptions of their construction. Comparing cartograms with traditional methods of cartographic presentation Hui Sun and Zhilin Li got results which cannot be surprising - the combination of cartogram with color filling of basic fields on quantity level (as in choropleth mapping) was evaluated as less useful in presenting phenomena than a traditional map in the form of a choropleth map. If however the color filling indicated quality information only (candidate support in elections) respondents evaluated the cartogram very favorably. It can thus be stated that cartograms are a form, which well presents quantity information in connection with color filling of spatial units illustrating qualitative data. When comparing types of value-by-area contiguous cartograms respondents were of the opinion that the diffusion contiguous cartogram and the pseudo-cartogram are most useful in presenting population phenomena. The last of the mentioned researches (I. Kaspar, S.l. Fabrikant and P. Freckmann 2011) shows that respondents had greater problems analyzing data presented in the form of a cartogram than on traditional maps. This was particularly visible in relation to questions on the general distribution of a phenomenon. It can thus be said that the efficiency of cartogram reception depends on the shape of basic units before and after transformation, applied algorithm, complexity of information which we want to attain from the map and the appropriateness of legend. Readability and interpretation of cartograms depends on the skills of both the cartographer and the addressee (B. Dent 1975).