Analysis of Pre-Geodetic Maps in Search of Construction Steps Details.

Regeneration of ancient cartography in digital form is an interesting way not only to preserve historical cartographic documents as a cultural heritage, but also to allow new chances of understanding and using the historical information they record. In such a way, modern digital techniques, in particular study of map deformations and georeferencing, help in metric analysis of ancient cartography, and at last they appear to be useful for researchers to derive historical information for their studies, for example related to urban development or to geomorphological and environmental topics. The present research would give an example of the usefulness of the digital regeneration of ancient cartography, coupled with a visual analysis of the drawing. The study subject is a set of three maps portraying the Po river delta area (Northern Adriatic Sea, South of Venice, Italy) at the end of the 16th century, today preserved in the Venice National Archive. As they depict different landforms of the easternmost peripheral areas that today no longer exist, they are compelling for a geomorphological analysis, and they constitute a very interesting case study. The three map samples, drawn by three famous land surveyors, were analysed and cross-compared to try to find out information concerning the late Renaissance land-surveying techniques and the related cartographic draft steps. The kinds of evidence taken into account consist of technical signs preserved either in the palimpsest of the maps or in their final drawing. The meaning of some signs is explained by the Authors themselves in the legend, whereas the meaning of others can be inferred by an interesting methodological textbook, written by the main author to describe a new topographical instrument invented and used by himself. All these signs highlight a very interesting class of information related to the hidden steps of pre-geodetic map construction, which up to now is probably still poorly known and studied. Furthermore, an unusual methodological tool, never applied to this kind of researches up to now, is here proposed, i.e. the splitting of the original cartographic drawing in some subareas and its relocation to overcome the local gross topographic inconsistencies recorded on the maps.