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Ocena programów GIS wykorzystywanych do opracowania kartograficznych anamorfoz powierzchniowych

Markowska A., Korycka-Skorupa J.

Polski Przegląd Kartograficzny

2015

T. 47, nr 1

21--32

W artykule omówiono programy komputerowe, służące do automatycznego opracowywania kartograficznych anamorfoz powierzchniowych. Poruszono kwestię algorytmów, na podstawie których można opracować różne typy anamorfoz powierzchniowych. Celem artykułu była również ocena dostępnego na rynku oprogramowania, służącego do generowania takich anamorfoz. Opracowując kartograficzne anamorfozy powierzchniowe należy zadecydować, jaki typ mapy chcemy otrzymać, a tym samym jaki należy zastosować algorytm. Kolejnym etapem jest wybór oprogramowania, które często uzależnione jest od wcześniej wybranego typu anamorfozy. Przedstawione w artykule programy są bezpłatne. Do wykonania anamorfoz w analizowanych programach wykorzystane zostały dane dotyczące wyborów prezydenckich w Polsce w 2010 roku. Na potrzeby badania wykonane zostały anamorfozy powierzchniowe Polski w podziale na województwa oraz mapy województwa mazowieckiego w podziale na powiaty. Wybrane programy zostały poddane wnikliwiej ocenie. Wyniki badań pokazały, że programami, które w największym stopniu spełniają założone kryteria są: Cartogram Utility for ArcGIS, Scape Toad oraz MapViewer 7. Przy opracowywaniu anamorfoz powierzchniowych ważny jest kształt otrzymywanej mapy. W zależności od zastosowanego geodezyjnego układu odniesienia można otrzymać różne anamorfozy – bardziej lub mniej przypominające geograficzne zarysy jednostek administracyjnych. Dlatego też należy dobierać układ geodezyjny w zależności od obszaru, a jeżeli nie jest to możliwe, to po opracowaniu mapa powinna być dopracowana w programach graficznych.

The purpose of this article is to report a study aimed at systematic assessment of the functionality of commercially available software for the automatic generation of area cartograms. The issue of the wide choice of algorithms developed over the years for generating various types of surfaces has also been raised. Cartograms (called also anamorphic maps) are constructed by changing the surface area of each spatial unit in step with the corresponding value of the mapped thematic variable (area cartogram) or changing accordingly the distance between the preselected focal point and other points on the map (distance cartogram). Depending on the shape of mapping units, the following three types of area cartograms can be distinguished: • proportional symbol cartogram were the original shapes of mapping units have been replaced with simple geometric shapes such as squares, rectangles or circles (for example, Dorling Circle Cartograms, square cartogram); • continuous regular cartograms where the shapes of areal units on the map resemble the actual shapes of the mapped units but their boundaries have been geometrized to consist of perpendicular sections; • continuous irregular cartograms where the shapes of areal units on the map resemble the actual shapes of the mapped units but unit boundaries are not straight lines. Cartograms can also be constructed to preserve spatial contiguity (continuous cartograms) or not (noncontinuous cartograms), with the latter often preserving the underlying neighborhood relationships to some degree. While constructing area cartogram, one needs to decide first the type of a surface to be developed, and therefore, the algorithm to be applied. The next step in map construction is the choice of software, where tool selection depends often on the predetermined type of the cartogram. The study surveyed five programs for the construction of area cartograms – all available free of charge. Each of those software tools was used to generate area cartograms portraying data from the 2010 presidential election in Poland. Two groups of areal cartograms where generated for the purpose of this study: maps of the entire Poland by voivodships, showing the number of valid votes cast for the two presidential candidates in each voivodship, and maps of the Mazowieckie voivodship by county, portraying the number of valid votes cast for the individual candidates in each county. The subsequent in-depth assessment of surveyed programs took into account eleven criteria including the number of cartogram types that might be developed using each program, availability of tools for the proper legend construction and display, possibility of supplementing the cartogram with complementary choropleth maps, the option for inserting map labels, the type of spatial data that can be used in the software (reference to points, lines, polygons) and so on. The study has demonstrated that the tool included in the ArcGIS (Cartogram Utility for ArcGIS) best met the survey criteria scoring 9 points. The application Scape Toad placed second (7.5 pts.), while MapViewer 7 came third (6.25 pts.). When generating cartograms in the available GIS programs, one should also pay attention to the visual qualities of the generated maps, and in particular, to the resemblance of shapes of spatial units on the map to the their actual geographic boundaries. Since the shape outlines obtained on the map vary depending on the underlying geodetic reference system, the best coordinate system for the mapped area should be selected. However, if such system cannot be used within a given cartogram generating tool, then the obtained cartogram should be exported and refined with some general software package for graphic editing.

Badania czytelności kartograficznych anamorfoz powierzchni

Faliszewska A.

Polski Przegląd Kartograficzny

2012

T. 44, nr 3

225-238

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).