Kartodiagram i kartogram a charakter danych - badania eksperymentalne

Poprawne stosowanie kartograficznych metod prezentacji warunkuje czytelność redagowanej mapy. Wiąże się z tym m. in. wybór odpowiednich danych statystycznych. Często sprawia on autorom map wiele trudności, dlatego stał się powodem niniejszych rozważań. W artykule przedstawiono próbę klasyfikacji danych za względu na ich charakter. Zaprezentowano poglądy kartografów związane ze stosowaniem danych do dwóch metod prezentacji: kartogramu i kartodiagramu. W dalszej części artukułu przedstawiono analizę danych na mapach w atlasach geograficznych oraz badania ankietowe, których celem było skonfrontowanie przedstawionych poglądów z praktyką kartograficzną.

Proper application of cartographic methods of presentation is a condition for map's readability. It is related to a choice of appropriate statistical data. The article presents an attempt to classify data by type (fig. 1). Absolute data is represented by absolute numbers. They can be divided into two groups: proper - simple data represented by absolute numbers and transformed, which despite undergoing a transformation (e.g. averaged in time or related to the whole set) are still absolute numbers. Relative data is represented in fraction form, in relation to a particular component. Relative data can be proper, shown as a fraction, and transformed. Data type is of significance when differentiating between two types of cartographic presentation: choropleth map and diagran map. In cartographic literature a lot has been written about the selection of data for choropleth map presentation. The choropleth map method is usually recommended for presentation of ralative data. Data selection for diagram map presentation is much more disputable. Most handbooks recommend absolute data. Unfortunately this recommendation is not supported with any evidence. Some authors allow also relative data, but they do not provide any evidence either. Therefore there is no specific advice as to which type of data should be chosen for diagram map presentation. This research tried to establish the practical solution to the problem of data selection. One of the methods is an analysis of maps published in geographic atlases. 3656 diagram maps from atlases have been analyzed in order to determine the type of data used for them. The results showed absolute data to be the majority (86,4% of analyzed diagram maps). Diagram map presentation of relative data was applied significantly less often (4% of the total number of diagram maps). Another method of establishing a connection between theory and cartographic practice is a survey. Survey questionnaires were distributed twice to geography students at Warsaw University and Higher School of Pedagogics in Kielce. The first survey was to establish the methods of data selection by individuals who had not been acquainted with the rules of cartography. The second survey, conducted after a oneyear cartography course, was to determine the application of theory in practice. There were two types of tasks. The first one was to invent map titles (an open task). In the second part students were given several titles and asked to decide, which of them could be presented on a particular map (a closed task). Maps in the questionnaire had to be perceived similarly by all participants and should not be associated with any real terrain. Therefore fictional maps had been prepared. The first survey included 178 students (100 from Warsaw, 78 from Kielce). It showed that data selection for diagram maps and choropleth maps is not intuitive. The participants asked to suggest map topics handled diagram maps rather well; the results for choropleth maps were worse. Detailed analysis of chosen topics showed that the students had difficulties with both methods. The participants could not differentiate between the two types of maps and often assigned to them the same topics and therefore the same data. The second survey included 158 participants ( 84 from warsaw, 74 from Kielce). In both groups there was an increase of the number of correct answers (fig.11). However the results in both centers were significantly different. In Warsaw there were more correct answers, while in KIelce only a decrease in the number of incorrect answers was evident. The conducted survey showed that data selection for the methods of cartographic presentation is not an easy task. Theoretical instructions quoted in handbooks are not intuitively followed by map users. Choropleth map presentation is usually connected with the application of relative data. Diagram maps usually show absolute data. This rule is respected in practice, alt-hough there are common exceptions. Some of the students, before as well as after the course, had different opinions-in the first survey unconsciously, basing in intuition or coincidence, in the second survey often consciously, claiming that particular data simply fit the map in question. Despite cartographic education not all the students acquired the rules. Different results in Warsaw and Kielce may suggest that cartography lecturers put different stress on this issue. However in both centers there is a visible improvement after the course has been completed. It can be assumed, that the results are more evident where the theory has been stressed more. In both schools, after the course had been completed, there was only a small number of incorrect or illogical answers. This shows that the students acquired presented knowledge. However in cartography some rules are more and some less logical. Presenting forests in green and waters in blue is beyond question. It is logical and obvious. Data selection for the methods of presentation is not as logical, therefore it is not as widely accepted.