Field survey and GIS

Training team

The Durham team was led by Prof. Anna Leone (Durham University) and the field activities coordinated by Dr. Marco Nebbia (Durham University), with the assistance of Dr. Tom Fitton (University of York) for the field survey, and of Ms. Particia Voke (Wessex Archaeology) who taught geophysical survey techniques, in particular magnetometry.

Training objectives

During the first year of training in July 2017 (Fig. 1), we developed a field survey strategy in order to investigate the coastal site of Iunca (Tunisia). The site of Punic foundation has Roman, Late Roman/Byzantine, Islamic and Late Medieval occupation phases and the surface material represent an ideal scenario for understanding different chronologies across the surveyed area. Already during season 2017, after processing the first set of field survey data, it was clear how the older part of the site lays in the northern part and how between the 4th – 5th century AD there is an ‘expansion’ to what is the full extension of the Roman settlement (Fig. 2).

 

 

 

 

 

 

 

 

 

 

 

Fig. 1 Overview of the field survey carried out in July 2017.   Fig.2 Overview of the chronological distributions at Iunca.

 

Starting from this previous knowledge of the archaeological area of Iunca, we planned the second season (September 2018) of field survey with a new group of participants (35) from INP and DOA. The aim in the second year was to train new people in the systematic site sampling strategy and to complete the survey of Iunca. This would allow a more complete understanding of the site extent that would help the INP in defining its limits and the boundary of the buffer zone, for protection purposes.

Training

The training in field survey was integrated with the training in GIS as the latter has been utilised to process the field data collection. Hence the course included both activities in the field as well as desk-based. During class sessions, the whole practice of survey planning, data collection and data processing has been widely covered and discussed.

The first week focussed on field survey techniques and specifically site-sampling and track-walking. A short introduction to the principles of archaeological field survey and how it has been used within the discipline for research purposes was followed by morning activities in the field, collecting surface material at Iunca. As in 2017 the 50m spacing and the sample radius of 1m have been maintained for consistency purposes.

Fig. 3 Overview of the results from two seasons of field data collection at Iunca (Tunisia).

The aim of completing the survey of the archaeological area of Iunca has been fulfilled within 4 mornings of fieldwork, thanks to the sheer number of participants and their fast learning skills.

We covered an area of approximately 170 ha for a total of 530 samples from which the 11 teams collected surface archaeological material. As we did last year in each team (3-4 people) someone was in charge of the hand-handle GPS in order to take the location of the sample, someone else to pick up and bag the artefacts, and the third person in charge of filling in the form (Fig. 4).

Fig. 4. Survey form developed from the Training in Action team, used during the training at Iunca.

The survey form contains basic information on the sample that we then used during the data processing to calibrate the quantities of surface material against variables such as ground visibility, land use, topography.

Following the same strategy of the previous season we decided to stop each transect after 4 empty samples, thus reaching a 200m zone of negligible archaeological material on the surface. This threshold has been chosen as in the Tunisian legislation the limit of 200m defines the buffer zone of a single site – after 200m we have a different archaeological site. This sparked a lively discussion among participants after the initial processing of the survey data (see below).

GIS

The afternoon sessions were dedicated to the processing of all the data collected in the field during the mornings. The GPS points have been imported into QGIS (see Fig. 3) so participants could appreciate the work done every day and understand the extent of the areas covered with the survey.

The material collected and bagged with labels have been handed over to the pottery team for the cataloguing training course.

An initial introduction to GIS, where basic concepts like coordinate systems, data types (vector and raster), and simple tools have been presented, was followed by regular sessions of post-fieldwork data processing. These included downloading GPS data from different devices and conversion into GIS format (shapefiles), data cleaning, and creation of attribute tables.

In the first couple of days, simple data import and visualization have been presented to the trainees as well as concepts like coordinate systems and map projections which are fundamental when working with spatial data in GIS. It seemed very useful visualising the even just the GPS points showing the location of sample areas, so that the participants appreciated and understood their efforts in the field; it is difficult to visualise and grasp the overall meaning of the field survey from the ground, therefore ‘a view from above’ that GIS allows, assisted enormously in appreciating the bigger scope of the survey.

Afterwards, we explored the more complicated process of cleaning GPS files, namely identifying and sorting mistakes and unusable information, in order to integrate it with the archaeological data coming from the pottery cataloguing training. The latter took place at the same time and therefore we were not able to integrate typological and chronological information into GIS at this point. However, we managed to import and work on the quantities, thus discussing the density of surface material across the site, integrating the data from both seasons (Fig. 5).

At this point with the complete survey of the whole archaeological area of Iunca we started a lengthy discussion on how to use and to interpret the distribution map in Fig. 5 for the definition of site limits and buffer zone. I asked the participants to draw a polygon on what they would think it was the edge of the archaeological site, and to what they would have conceived to be the buffer zone of Iunca.

The proposed answers to the first question were varied, but all the trainees grasped the sense of this exercise and the value of such field method to establish more thoroughly the extent of such large archaeological site. Further debate sparked from the answer to the second question of the definition of the buffer zone, as the discussion focussed mostly on the South-East corner of the site (see Fig. 6).

The fact that there was still substantial surface material found beyond the 200m defined by the Tunisian as threshold to consider to define two different sites, brought some participant to agree in considering that area as a separate archaeological site; however, the fact that those surface remains were mostly to be attributed to sub-urban/rural building associated to the ‘main’ Roman town/citadel (because of the similar chronology of the pottery), brought some other participants to consider that area as part of the site of Iunca itself and not as a different one. The discussion didn’t reach an agreement on this point, but on the fact that further fieldwork is needed to better assess the situation in the southern part of the site.

Fig. 5. Overview of the quantities of surface material in each of the surveyed samples in both field seasons 2017-18 at Iunca (Tunisia). Image source: Pleiades 4-bands; 0.50m resolution.

Fig. 6. Overview of the proposed site limits (in red) and buffer zone (in green) of Iunca (Tunisia).

This is a great result as it shows how the method of field survey and GIS has been taught and critically discussed in its application for the definition of site boundaries and buffer zone, which are two of the main aim of the training in field survey techniques. I deem that the take away point is that any methods and techniques that are being taught needs to be flexible enough to be customized and tailored to specific legislations that are in place in different countries. With the added value though, that these methods can also allow for the legislation to be revised if necessary and if there is will in doing that from the local authorities in charge of the documentation and protection of the Cultural Heritage.