Czytelność kartogramów prostych i złożonych - badania eksperymentalne

W artykule omówiony został eksperyment przeprowadzony z udziałem użytkowników map, którego celem było porównanie kartogramów prostych i złożonych pod względem czytelności informacji o rozmieszczeniu zjawisk oraz informacji o zależności zjawisk. Uzyskane wyniki świadczą o tym, że kartogramy złożone są dobrze czytelną formą prezentacji zależności zjawisk, co weryfikuje dotychczasowe poglądy kartografów.

Two-variable choropleth method allows to present two different quantitative variables on the same map. The purpose of such mapping technique is to visualize geographic relationship. Readers' perception is considered to be an important limitation of two-variable choropleth maps. The negative opinion about the effectiveness of this form of presentation is based on maps published in the 1970s by the U. S. Bureau of the Census. Poor readability of Census maps results from an inappropriate graphic representation and it was evidenced experimentally (J. Olson 1981). In order to check improperly designed two-variable chorpleth maps can be well understood by their readers, an experimental test was conducted, in which the effectiveness of one-variable and two-variable solution was compared. It was checked if one-variable maps are more appropriate to show spatial distribution and if two-variable maps make the geographic relationship easier to interpret. The participants were 128 students of geography at Warsaw University. They performed different typical map-reading tasks on one-variable and two-variable choropleth maps. The students were divided into two groups. Each student performed the test twice, each time using a different type of maps - the first group worked with one-variable maps first, the second group worked with two-variable maps first. In order to design comprehensive two-variable maps a complementary color scheme, proposed by J.R. Eyton (1984), was used and number of classes was limited to 9 (3x3). The maps created for experiment looked like the actual census maps. The test consisted of six tasks. The students were asked to extract from maps information about distributions (tasks Rp1, Rp2, Rp3) and variables relationship (tasks Zp1, Zp2, Zp3). Questions were asked about specific as well as about general information; they referred to individual enumeration units, regions and whole maps. As a test result the percentage of correct responses was calculated. At the end of the experiment students expressed their opinions and preferences about both types of maps. The results of this experiment verify opinion about poor readability of two-variable choropleth maps. Students were more accurate in reading spatial distribution on one-variable maps (especially the general pattern) and in reading spatial relationship (at every level of perception) on two-variable maps. They found two-variable maps a little bit more difficult to interpret but this form of presentation seemed more unusual and interesting. They found also that one-variable solution is more appropriate to read distribution and two-variable solution - to read variables relationship. These results showed that two-variable maps, if properly designed, can be quite properly interpreted by map readers and can be useful in visual exploration of geographical data, especially when the relationship between phenomena is crucial.