Gustav Forstner and Markus Oehrli:
Graphic representations of the analysis of old maps and the development of distortion grids
Cartographica Helvetica 17 (1998) 35–43
Graphic representations are often used to show the accuracy or the errors of early maps. The methods used today (distortion vectors, iso-deformation, coastline matching, circle method, etc.) are described briefly and shown with examples. Papers and reports treating such representations are listed in an appendix.
The construction of distortion grids is one of the oldest methods known. Such grids were introduced by Hermann Wagner at the end of the 19th century. His so-called 'cartometric method' was used quite often until the First World War, after which it disappeared. Eduard Imhof re-used the distortion grid method in 1939 to analyse old Swiss maps.