TOPOGRAPHY - Research

Superimposing antiquarian maps

Nelly Martin, last up-date August 2002

There is no real shortage of old and antiquarian maps representing Alexandria, both ancient and modern, and the archaeologists are particularly interested in superimposing them upon the digitised cadastral map of the city and thus extracting a maximum of information. However, this superimposition is not so easy. The localisations established from these old maps can prove to be very uncertain.

Detail from the map of Mahmoud Bey el Falaki (1865) - © CEA

After a long period of research a computer programme to deal with these old maps was developed in 2000 which allows for the superimposition of the scanned maps (raster) onto the Alexandrian cadastral map (vector) using as intermediaries the programmes MapInfo and Surfer. The old map is deformed as a function of certain chosen salient points (landmarks) upon the map.
Choice of fixation points on a detail of the map of Gratien Le Père (1798) - © CEA

Once the geometric realignment of the maps has been achieved, they can be integrated into the Geographic Information System (GIS).
Superimposition of an old map (in black) upon the digitised cadastral map (in red) - © CEA