Thursday, September 03, 2009

Using Edge Detection Algorithms to Search for the
Physical Remains of Roman Centuriation and Surveying

But the land surveyor is like a judge; the deserted fields become his forum,
crowded with eager spectators. You would fancy him a madman when you see
him walking along the most devious paths.


It is well known that the remains of Roman Surveying throughout Northern Tunisia are the best preserved in the world, but the difficulties in geographically locating these areas has led to a serious lack of research and scholarship on these remains. The Romans, in the regions around Carthage, Dougga and Enfida, surveyed extensive areas, and left behind physical remains in the form of limites and field boundaries. I have recently begun studying these regions using both fieldwork and computer methods in an attempt to locate and map these important remnants of Roman colonization. In the figure below I have used an edge detection algorithm on a satellite photograph (Landsat) of the area around Carthage that allows for the enhancement of linear field boundary features and whose results can be statistically compared to the known forms of Roman cadastral surveys found in texts such as the Corpus Agrimensorum.

[click on figures to enlarge]

Once the extent and size of these 'survey areas' has been determined a grid can be fitted and overlaid on a satellite photograph of the region in question. The figure below shows the area around the modern town of Enfida, Tunisia. The calculated grid lines up quite well with the current local path system around the fields and with the intersection known to have been the kardo and decumanus in Roman times.

Below one can see a GIS map that I produced showing several of the areas studied so far using these methods along with a grid over the approximate extent of the physical remains. More complicated algorithms using both Fourier and Radon transforms have also been used to locate and orient the regions shown. I have presented detailed results of this research at the International Conference on the History of Cartography held in Copenhagen in July of 2009, and will provide more on the mathematical details of this in a future post and publication.