GIS AND HISTORICAL CARTOGRAPHY IN COASTAL ZONES: INTEGRATION OF DIFFERENT SOURCES TO ANALYSE LANDSCAPE TRANSFORMATION PROCESSES

Michele De Silva

Dipartimento di Archeologia e Storia delle Arti, Università degli Studi di Siena (IT)

Slide 1
My name is Michele De Silva. I am professor in Geography at the University of Florence and PhD student in Medieval Archaeology at the University of Siena. My fields of interest are historical Geography and Landscape Archaeology. At the moment I'm studying the historical transformations of the landscape and of the settlement patterns in the Grosseto coastal belt in Southern Tuscany as a part of the PhD research and as a contribute for the MEDCORE Project.

Slide 2
The research, still in progress, has two main goals: On one hand to setting up a methodology for the study of the ancient landscape using different kind of sources integrated in a GIS environment with special reference to historical cartography and aerial photo. On the other hand to apply this methodology for better understand landscape transformation processes and the historical evolution of settlement patterns in the Grosseto coastal belt.

Slide 3
In this paper I would like to point out:

• The role of historical cartography as a source of information in landscape archaeology studies;
• Then the increasing of its potentialities by the integration with other sources;
• And finally the methodological backward research approach via the presentation of Grosseto Plane case study.

Slide 4
First of all we would like to focus our attention on historical cartography as a document representing the archaeological map of the time in which it has been realised. In fact, *maps represent the territorial settings related to the time of their realisation and moreover *they may show traces of ancient or previous settings. In some good examples maps can also highlight the position of ruins or archaeological evidence providing useful information on their existence and position. Furthermore,* as an historical document and human product, historical cartography needs to be interpreted in terms of direct and indirect information which can be offered to scholars today. In particular, the data that are represented and marked in the map needs to be checked and verified as regarding their characteristics and their position. In fact maps represent in a symbolic and iconographic way the reality of the landscape of the past as it was perceived by the ancient cartographers.

Slide5
In order to undertake comparison and interpretation of the historical maps we can develop two parallel and complementary directions; analysing the document from a semiotic and anthropological perspective and develop analysis from a historical and geographical point of view. In this paper I am going to present mostly the second direction of analysis.

Slide 6
Historical cartography presents a wide range of typology of maps which can be ordered in terms of scale, themes, techniques of representation and so on; perspective representation or view bird scenes cause several difficulties in georeferencing maps even if they are very stimulating as regards the perception of the landscape; but [Slide 7] in the case of GIS analysis it is important to subdivide historical cartography in terms of its geometrical characteristics: geometrical maps, and in particular the cadastral maps of the eighteen and nineteen centuries, are fundamental examples of geometric accuracy (useful in GIS application) offering detailed information and richness in thematic data. In order to carry on the research it is important to use different kinds of sources, integrating them into the GIS, exploiting the potentiality of thematic and spatial overlay. In other words, it is necessary to correlate the study of ancient maps with other information derived by recent maps and aerial photographs. In particular it is remarkably important to compare today's photos with the historical ones.

Slide 8
The methodological approach proposed in this paper is based on the regressive historical geographical analysis. Research is developed starting from the analysis * of today's landscape settings (here the city of Grosseto), going backward to the interpretation of the settings of the past throughout the individuation of regressive phasing *. In this way landscape settings are sliced in their historical stratification proceeding backwards, as in an archaological excavation, from the most recent to the most ancient *.

Slide 9
In this paper I am going to present some examples extracted by a work in progress case study in which I have utilized the Catasto Lorenese, a geometric Cadaster carried out for the whole territory of Granducato of Tuscany between eighteen seventeen (1817) and eighteen thirty-five (1835). The Catasto Lorenese is particularly rich in detailed information documented in form of maps, in form of records in tables and inventories, and in a descriptive form in related texts. Maps are really thick of data and allow a good and accurate georeferenziation avoiding the introduction of too strong deformation of the features represented in the document.

Slide 10
The elements which are particularly remarkable for our studies are *the "quadri d'insieme", that is to say general frameworks topographic maps varying in the scale from one to twenty-five thousand (1:25000) to one to eighty thousand (1:80000), and * the "fogli", detailed *maps at a scale of 1:2500.

Slide11
Other sources utilised in this research include mainly:

• Archaeological evidence derived from literature mainly focused on prehistoric, protohistoric, etruscan and roman periods
• eighteen century historical cartographies analysed by Paolo Marcaccini
• Historical Cadastral maps edited in eighteen twenty for the Comunità di Grosseto
• IGM Cartography edited bt Military Geographic Institute in eighteen eightytree (1883) at scale one to fifty thousand (1: 50000)
• Topographical maps edited by Regione Toscana at scale one to ten thousand (1:10000)
• Atlante diacronico delle coste toscane fifties - eighties edited by Regione Toscana
• Two Aerial photography series: the recent one is the ortophoto AIMA, at a nominal scale of one to ten thousand (1:10000) which provides information for the landscape settings of the ninety's.

For the previous settings, that is to say how the landscape appears before the large transformation occurred during the sixties, I have chosen the VOLO GAI, shot in Tuscany in the nineteen fifty-four (1954) referable to a scale of one to thirty-three thousands (1:33000).

Slide 12
Let's start in presenting the Grosseto coastal plane located in southern Tuscany.

Slide 13
it is a wetland area. A large part of it was occupied* during * Etruscan and roman period by Prile Lake .The archaeological sites of Vetulonia * and Roselle * were facing the lake shore. After the roman period the lake progressively turned into a fenland. Since Medici time till the last century the area was interested by a series of important reclamation and drainage activities.

Slide 14
Here is a reconstruction undertaken by Paolo Marcaccini (of the Florence University) of the wetland settings during the eighteen century (theamtic layer in blu). It is based on the analysis of histhorical cartography and aerial photos. During this century the marsh was still occupying a large part of the coastal plane on the west side of Grosseto.

Slide 15
In order to analyse the general settings of the beginning of the nineteenth century I have used the Quadro d'unione of the Catasto Lorenese drawn at a scale of 1:60000 (one to sixty thousand). This historical source like, the others previous mentioned, have been georeferenced and input into the GIS. Even if this document is a cadstral map the historical cartographers paid a lot of attention in drawing the hydrological settings and the reclamation works. They also demonstrated a particual interest in defining the different nature of wetlands, distinguishing the "chiari", that is to say deep water areas and free from vegetation growth, and channels from the general marsh.

Slide 16
Different kind of information have been interpreted and thematic layers have been digitised. The slide shows wetlands and main drainage system as it is represented in the map.

Slide 17
The reclamation works occurred since the end of eighteen century obtained only partial success also due to opposite social needs: on one hand to maintain the exploitation of fenland resources (mainly fishing activities) on the other hand to fight against marsh fever diffusion and obtain lands for agriculture activities.
Nevertheless the small scale of the map, it is possible to appreciate changes in coastline (here in red the coastline of eighteen twenty)

Slide 18
In order to appreciate changes occurred during the nineteen century we have input into the GIS the IGM topographical maps (at scale one to fifty-thousand) edited in the 1883 (eighteen eighty-tree). These maps reveal a more homogeneous and symbolic way of representing landscape characteristics.

Slide 19
Also in this case, hydrology and coastline have been digitised from the maps. The acquisition of these layers highlights the new drainage network of Grosseto plane.

Slide 20
Drainage works and a new deviation channel of Ombrone River, relaised on the north side of Grosseto [show], contributed to obtain a further reduction of a large part of wetlands.

Slide 21
The present hydrological settings of Grosseto coastal plane, here represented in details derived from the carta tecnica regionale at a scale of one to ten thousand (1:10000), still shows the general framework structure inherited from the past. This slide also shows the erosional trend of the coastline during the last fifty years. Green indicates the advancing of the coast, red indicates an erosional phase, blu indicates no changes.

Slide 22
Next slide series summarise the progressive reduction of wetland areas throughtout time:
Situation during etruscan period
*The eighteen century
*The beginning of nineteen century
*The end of nineteen
*Today settings

Slide 23
This is an overlay showing different extent of wetlands through time from more ancient, represented in pale blu, to the present day settings, in dark blu.

Slide 24
We are now shifting from a general framework to a more detailed analysis of the landscape transformation developed through the integration of different sources. Now I am focusing just on few examples regarding the southern part of the study area. For these case studies we have used the aerial photos series Aima and * GAI, and * Catasto Lorenese.

Slide 25
In centre of the aerial photo of nineteen ninety-seven (1997) we can see, from north to south, a channel tributary of Ombrone River; actually we can not see any traces of old watercourse *. instead the photo of nineteen fifty-four (1954) shows evidence of an old sinuous watercourse already reduced to the channel. On the contrary * the historical cadastral maps of eighteen twenty (1820) describe a different situation, showing the natural water course.

Slide 26
The second example concerns study on coastal changes. The good geometrical characteristics of the lorenese cadastre allow to perform accurate analysis on the extent of lakes and on see shorelines. The example show the erosional trend, going backward in time from nineteen ninety-seven (1997) * , to nineteen fifty-five (1954) * to eighteen twenty (1820), of the river Ombrone's mouth and the relative coastline, which moved back about 1 km since eighteen twenty (1820).

Slide 27
The third example concerns understanding archaeological evidence by integrating different sources. The cadastral maps of eighteen twenty (1820) and their Quadro d'unione, shown in the slide, testify * * the presence of remains of Aemilia Scauri roman road, also called Aurelia. The symbol of interrupted line adopted by historical cartographers to draw the feature, and the text line on the map "tracce dell'antica via Aurelia" indicate that the road was not in use in the early nineteenth (19th) century. The detailed map one to five thousand (1:5000) indicates also * presence of ruins "rovine del ponte del diavolo" located on the edge of the Ombrone River last meander, which the ancient maps named * as "volta ai marmi" that means something like "turn of marbles" a clear reference to the presence of a roman bridge. * In nineteen ninety-seven (1997) aerial photos, the traces of the roman road are almost disappeared, * instead looking at nineteen fifty-four (1954) aerial photos * these traces are very sharp *, as we can see * better zooming in *. We are expecting that older photos of the first half of the twentieth (20th) century, that we have planned to analyse, will offer results even more exciting.

Slide 28
Here we show the road network derived by the lorenese cadastre of the southern Tuscany coastal belt. Few years ago we have analysed this network from a morphological point of view, in order to highlight anomalies which can witness road segments belonging to a higher rank, or which have an older origin then the local inter-village road network. In black are drawn network anomalies that are not referable to sheep way of transhumance. Today, * if we compare some of this anomalies with evidence derived from historical cartography and aerial photos, we can recognize some of these segments as a part of the roman ways.

Slide 29

Let's go straight to the conclusion.
I think that We have to take into consideration Landscape not in a synchronic way but as the dynamic result of an historical sedimentation process, in which different events have left traces one over the others, becoming a complex as a whole. The Reverse Research method of analysis, together with the integration of different sources through GIS tecnologies, allows us to display separate layers of historical sedimentation.
In this perspective, the use of georeferenced historical cartography in a GIS environment, opens stimulating research potentialities in studies of the trasformation processes in coastal zones.

Slide 30
From the integrated analysis of aerial photos (especially of the past) and historical cartography we can obtain many information that can be of different kinds, explicit and latent. This type of analysis highlights if, sometimes when, but exactly where something interesting, in an archaeological perspective, took place. In this paper we are going to show just few examples from this case study.