Abstract:

Determination of the centre of the city or agglomeration or generally the geographic area is a task which is often undertaken as part of the promotional actions realized by local authorities or directly by inhabitants. Nowadays, especially due to the development and availability of positioning technology and satellite imaging, this job is undertaken within the framework of general didactic tasks and group projects during the study course in the field of geography, spatial planning, geographic information systems (GIS), but mainly geodesy and cartography. The task can be solved using the properties of a topological space or in Euclidean or metric space. The example given in the article was practically completed by the Scientific Hevelius Circle at the Technical University of Gdansk and it referred to the centre of the Tricity agglomeration (Trójmiasto - Gdańsk, Gdynia, Sopot in Poland).

At the same time, due to the availability of precise geodetic measurements, it is expected to indicate the exact position of the centre of the geographic area. By restricting the analysis only to geodetic or mathematical centre of the area and excluding the semantic centres, related to e.g. population density or intensity of communication development, anyways there are many variants of the centre of agglomeration determination method and assumptions. It is known problem of selecting the type of centre: It is possible to distinguish between the geographic and geometric centre also extended to the city centre of gravity (taken differently also as the centre of mass in the context of physics issues). It is also possible to analyse the determination of centre in the spatial context (including terrain shape), but also on the plane (de facto on the map created according to the chosen cartographic projection) or on the surface of the solid which approximates the area (depending on the size of the area this can be a segment of sphere, ellipsoid or geoid surface). It seems to be particularly easy to calculate the agglomeration centre realized with the use of digital maps. But it has to be kept in mind that this centre will actually be just the centre of area presented on the map and thus the imaging encumbered by mapping distortions (cartographic projection), and it may not ideally represent the physical centre of agglomeration in the field. This problem depends on the selection of cartographic mapping (and the resulting coordinates taken into account in the calculation of the city centre) and the location of the analysed area of the city in the cartographic mapping. In connection with the possible asymmetry and non-convexity of the shape which describes the city area, it may be impossible to indicate a specific, selected type of the centre within the city area. In such situations, despite the precise determination of area boundaries and use of correct methods for the agglomeration centre determination, it is necessary to choose such type of centre that it can be recognized by social and promotional expectations of the city. Article is therefore aimed to indicate the methods of determining the centre of agglomeration and on the other hand to select the method depending on the shape of the analysed area. The problems described in the authors’ consideration are important in spatial analyses (for the purposes of spatial development) and in the context of the use of cartographic and topological studies as a reference base for agglomerations and cities in GIS.

Keywords:

City centre, GIS, student group projects.