Philipp von Cranach:
Old maps as references
Cartographica Helvetica 22 (2000) 31–42
Old maps are important references for the historic research of geographic or topographic subjects. For the interpretation of these references the same rules apply as to any other reference. First of all it should be examined if and to what extent the map author may have been influenced by the objective or special interest of his product, and was possibly concentrated on specific contents, thereby knowingly or unwittingly omitting certain details. Especially with respect to these questions, historic research of local areas is often not very critical. One has the impression that the extraordinary achievements by modern Swiss cartographers has lead researchers to the assumption that former cartographers were also very «objective» with their representation of the topographic and geographic features. (Incidentally: our modern maps are probably also a product of specific aspects and one may assume that future historians will qualify the image of the 'quasi neutral data').
A further problem encountered in evaluating old maps is the relationship between the initial topographic survey and the subsequent final draft of the map. Since many maps are partially or totally based on older maps or surveys, any number of geographic or topographic elements such as roads, bridges or boundaries may not be contained in the final maps. Therefore, special attention must be paid to the identification and dating of old maps. Often only a few maps of a certain area still exist, which would imply that for various topographic or geographic features the exact same terms would inevitably apply if no other sources or references are available. At a first glance an objective reader may find this a fairly undifferentiated approach; however, the specialist will realize that this is the correct application of the historical method.
In researching the historical development of traffic networks and the cultural landscape, one of the tasks is to transpose the contents of an old map into a modern map or terrain. Since many older maps are neither equal area nor conformal projections due to the inaccurate surveying methods, such transpositions are usually quite complicated. One promising method calls for the unequivocal identification of still-existing control points in the old maps. A deductive iteration will usually lead to the identification of the remaining structural elements. Contradictions may arise when using different control points, but they can usually be solved if as many as possible old maps are consulted.