| Similarly to other themapic map types, geological maps are almost always compiled in a pre-designed topographic base. This method was also applied in case of the historical version of geological maps; the field observations and interpretations were signed in a base topographic map. This contribution provides a short overview of the topographic bases used at the different Hungarian historical geological maps from the 18th century to the WWII. The topographic basis is a key to geo-reference these maps, allowing their GIS integration and the spatial analysis of the knowledge evolution of the Hungarian geology.
A quite interesting and less discussed aspect of the geodetic background of these maps is the usage of prime meridians. The London meridian was used quite early at a geological map of Hungary, compiled by Townson (1797). Later, the prime meridian of Ferro was widely used, similarly to the maps of the continental Europe. However, the Ferro meridian is the meridian of Paris, increased by 20 degrees in round numbers. The real introduction of the Greenwich meridian occured only in the first half of the 20th century in the Hungarian topographic, thus also in the geological maps. |