Prezentacja zależności zjawisk metodą kartogramu złożonego

Artukuł poświęcony jest ocenie możliwości zastosowania metody kartogramu złożonego do przedstawiania zależności zjawisk. Omówione zostały zagadnienia metodyczne związane z opracowywaniem kartogramów złożonych. Zwrócono uwagę na problem czytelności tych map.

Presentation of information about geographic environment in a form of the maps of single phenomena does not always allow for a correct interpretation of relations between them. Simultaneous reading and comparing of several maps is often too difficult for perception of an average reader. Therefore one should look for more synthetic presentation methods, which instead of elementary information - about phenomena distribution, would present transformed information - e.g. about their relations. A two-variable choropleth map can be such a method. Its main feature is, that it presents values of two geographic phenomena within an areal units on map. The article discusses main methodic aspects of two-variable choropleth map elaboration. These are: choise of phenomena to be presented, preparation of a statistical scattergram, which is the basis for class intervals selection, and classification method. The author also presents principles, which should govern the process of planning a graphical solution suitable for the presentation of two variables. A color legend of a two-variable choropleth map used by the U.S. Bureau of the Census in the seventies is an example of such a solution. Poor readability of maps prepared with it suggests that further modifications of this legend are needed. Functioning of two-variable choropleth maps are the main source of limitations of this method. It is impossible to present phenomena distribution and relations at the same time. Thus a two-variable choropleth map should be seen as a compromise. Poor legibility of maps prepared with this method is a source of serious doubts. It has been proved through experimental research (H. Weiner, C.M. Francolini 1980, J. Olson 1981). The reading process can be improved through limiting the number of classes, application of proper graphic solutions and developing a clear legend. Reader's experience with such maps also plays an inoportant role. There necessary, the presentation method should be explained.