Cartographic heritage: toward unconventional methods for quantitative analysis of pre-geodetic maps

Historical cartography all over the world is a fundamental part of Cultural Heritage, and it needs to bepreserved from damage of its analogical support due to ageing. Regeneration of ancient cartography indigital form is an interesting way not only to preserve historical cartographic documents as Cultural Her-itage, but also to allow new chances of understanding and using the historical information they record. Insuch a way, modern digital techniques, in particular study of map deformations and map georeferencing,help in metric analysis of ancient cartography, and at last they appear to be useful for researchers toderive historical information for their studies, for example related to urban development or to geomor-phological and environmental topics. The present research would give an example of the usefulness ofthe digital regeneration of ancient cartography, but also an example of possible difficulties in correctlyinterpreting information preserved in historical cartography, especially the pre-geodetic one. The studysubject consists in three contemporaneous pre-geodetic maps (late 16th century) from the ancient Poriver delta area (Italy), by means of which a geometrically correct representation of those parts of thelandscape, not preserved today because of sea erosion, was tried. In fact, standard georeferencing meth-ods, that use reference control points to compare historical cartography with the present one, in thisspecific case demonstrated to be not successful in describing the real location of disappeared landscapedetails with an adequate level of accuracy. For these reasons, in order to define which map among theothers was the most faithful to the contemporaneous physical reality, a compound methodology, consist-ing of a three-step analytical process, is here applied to the three samples. Starting from measurementof sighting angles and distances applied to a number of landmarks, a splitting of the old maps in sub-areas, probably corresponding to the set of original surveyed zones, was performed. In the area of mainconcern, the use of absolute measurements was avoided in order to check the level of inner congruenceof the representation. Finally, a new specific error index, that can also be applied to maps lacking anexplicit graphical scale, is proposed to evaluate the map truthfulness degree. The proposed method canbe applied to other similar examples from ancient cartography.