# Digital Transformation of the Elymological Dictionary of Geographical Names
## 3 Model Design
### Georeferences
Incidentally, the use of a centroid can cause a discrepancy between the original and computed locations, but also errors in topology. It happens that the center of gravity of a city located on a river shifts from one side to the other as the borders change. Some entries in SENSG hold references to maps or atlases. However, other resources might be considered as well. Many old maps have been digitized and can be used to determine toponyms' geographic locations that are not found in official sources. It is enough to georectify these maps and read the coordinates of recognized objects. However, selecting a proper coordinate reference system and applying correct, accurate conversion when integrating various data sources is crucial. In Poland, for example, the 1992 National Projected Coordinate Reference System, PL-1992 (ETRS89/Poland CS92, EPGS:2180), is used for topographic maps at a scale of 1:10,000 and smaller. This plain orthogonal coordinate system was officially introduced through the Council of Ministers' decree in 2000 [39] (with further updates). It resulted from works started at the beginning of the 1990s, including Poland's territory in the European system of spatial references (ETRS) with the ETRF'89 system and the GRS-80 ellipsoid. It is based on a geocentric ellipsoid, GRS-80 (practically insignificantly different from the WGS-84 ellipsoid), and a Gauss-Kruger projection in one ten-degree zone (enough for the whole territory of Poland), with a meridian axial \(L_{o}=19^{\circ}\) and a scale factor \(m_{o}=0.9993\). The linear distortions range from \(-70\) cm/km in the central meridian to about +90 cm/km on the country's edges. The EPSG:2180 definition is publicly available in WKT format ([[https://epsg.io/2180](https://epsg.io/2180)]([https://epsg.io/2180](https://epsg.io/2180))), and many GIS (Geographic Information System) tools support algorithms for coordinates conversion. For illustrative purposes, an old map published in 1939 with the name Altkemnitz was found on the Mapster website ([[http://mapy.amzp.pl/tk25_list.cgi?show=5059](http://mapy.amzp.pl/tk25_list.cgi?show=5059)]([http://mapy.amzp.pl/tk25_list.cgi?show=5059](http://mapy.amzp.pl/tk25_list.cgi?show=5059));sort=w) and processed. Figure 8b shows the fragment of that map after georectification using the QuantumGIS software. This software was able to do the conversion between different coordinate systems (EPSG:4326 and EPSG:2180) on the fly. The points obtained from  
Figure 8: Map of Stara Kamienica: (**a**) Retrieved from the OpenStreet Map service (in EPSG:4326). (**b**) Retrieved from the Mapster website and georectified (in EPSG:2180). The point obtained from Wikipedia is shown with a marker in (**a**) and is labeled with A in (**b**). The point labeled with B in (**b**) represents the correct location as delivered by _Paufstwouy Rejestr Nazw Geografcznych_ (PRNG: “National Register of Geographical Names”). Wikipedia (A) and PRNG (B) are depicted. As confirmed, using an old map for geolocation discovery can end up with the same results as delivered from PRNG (the distortions caused by coordinate conversion are negligible). This example shows another essential issue. The castle presented on the map has survived to modern times. It can be found on a modern map, so the results of geolocation discovery can be verified. However, quite often, the objects of interest presented on old maps no longer exist.