GIS and Intra-Site Spatial Analyses: An Integrated Approach for Recording and Analyzing the Fossil Deposits at Casablanca Prehistoric Sites (Morocco)

doi:10.4236/jgis.2011.34036

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Journal of Geographic Information System, 2011, 3, 373-381

doi:10.4236/jgis.2011.34036 Published Online October 2011 (http://www.SciRP.org/journal/jgis)

GIS and Intra-Site Spatial Analyses: An Integrated

Approach for Recording and Analyzing the Fossil Deposits

at Casablanca Prehistoric Sites (Morocco)

Rosalia Gallotti1, Abderrahim Mohib2, Mosshine El Graoui2, Fatima Zohra Sbihi-Alaoui2,

Jean-Paul Raynal1,3

1Université Bordeaux 1, Bordeaux, France

2Direction d u Patrimoine, Institut National des Sciences de l’Archéo logie et du Patrimoine, Rabat, Morocco

3Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany

E-mail: [email protected]

Received June 3, 2011; revised July 23, 2011; accepted August 1, 2011

Abstract

The Mio-Plio-Pleistocene sequence at Casablanca, covering the last six million years, is well known in sci-

entific literature. The variability and the chronology of the Acheulian sequence is documented by systematic,

modern and controlled investigations in various sites (Unit L and Hominid Cave at Thomas I Quarry, Rhi-

noceros Cave at Oulad Hamida 1 Quarry, Sidi Abderrahman Extension Quarry, Bear’s Cave and Cap

Chatelier at Sidi Abderrahman Quarry) which have taken place within the framework of the

Franco-Moroccan co-operative project “Casablanca”. In order to manage the excavation data and to explore

the taphonomic nature of Unit L, Hominid Cave and Rhinoceros Cave, where research is still in progress, an

approach combining a Geographic Information System (GIS) and spatial analysis techniques was developed,

incorporating all existing information produced from previous excavations and recent surveys of the sites.

The amalgamation of this data into a GIS has resulted in a digital database that allows the production of si-

multaneous or separate visualizations and analyses of the fossils, artifacts and geological materials within

their original spatial contexts and also permits intra-site spatial analyses that allow a co mprehensive investi-

gation of the site formation processes.

Keywords: Morocco, Casablanca, Prehistoric Archaeology, GIS, Intra-Site Spatial Analyses, Site Formation

Processes

1. Introduction

During the last few decades archaeological research has

been characterized by a remarkable increase in the use of

computerised techniques; in particular, GIS (Geographi-

cal Information System) softwares have gained special

favour firstly in providing systems for the management

of archaeological data, and secondly as a fundamental

tool for the interpretation of archaeological contexts. GIS

has long been employed in archaeological landscape

studies for inter-site analyses. In recent times, many ap-

plications aimed at the interpretation of prehistoric de-

posits have also been developed [1-8]. The close connec-

tion between the spatial location of widespread exca-

vated evidences and the analytical study of each individ-

ual find makes the use of computer spatial analysis

technologies especially useful in conjunction with GIS.

In this intra-site application field, GIS plays a decisive

role in the identification of the spatial trends of archaeo-

logical data through the contextual or selective treatment

of spatial variables. The sp atial distribution of finds in an

Early Pleistocene site is largely determined by post-

depositional disturbance phenomena affecting the ta-

phonomic environment, whether or not they are anthro-

pogenic, which always need to be taken into account in

any spatial interpretation [9]. One of the most complex

problems to solve is overcoming the difficulty of recog-

nizing the sequence of these alteration phenomena,

which often occur simultaneously, and are hence hard to

differentiate in an overall analysis.

Intra-site spatial analyses are important methodologies

for unraveling the formation and sequencing of prehis-

R. GALLOTTI ET AL.

374

toric deposits, whose reconstruction provides decisive

evidence for the validation of subsequent deductive

analyses [10]. Thus spatial analyses make an important

contribution to the interpretation of prehistoric sites ex-

plored extensively using the stratigraphic method. In

consideration of the multiplicity of the above-listed fac-

tors, multidimensional analyses presently appear to be

the most advanced and appropriate techniques of spatial

investigation [11-17].

These considerations prompted our adoption of a

GIS-based investigation, integrated with spatial tech-

niques for the management and processing of spatial and

alpha-numerical data concerning the following sites of

the Casablanca region: Unit L and Hominid Cave at

Thomas I Quarry and Rhinoceros Cave at Oulad Hamida

1 Quarry. Investigations in these sites are still in progress

and this allowed us to design data management schemes

that followed each phase of the research rather than a

posteriori. In this paper we present the structure of our

information applications, the data recording system and

the types of analysis that we perform and envisage per-

forming.

2. The Archaeological Context

The Casablanca region on the Atlantic coast of the Mo-

roccan Meseta is rich in Palaeolithic sites p reserved in an

exceptionally well developed series of littoral deposits

(Figure 1) [18]. The Lower-Middle Pleistocene transi-

tion is well illustrated in Thomas I Quarry (Figure 2)

where the oldest lithic assemblages of the Casablanca

sequence are found in late Lower Pleistocene deposits,

circa 1 Myr in Unit L on an excavation surface of about

1000 m2, and consist of Acheulian artifacts made on

quartzite and flint [19]. In the same quarry, the archaeo-

logical assemblage of Unit 4 of the Hominid Cave,

where hominid fossils were first brought to light in 1994,

documents the Middle Pleistocene record. While this

cavity sheltered a population of hominids during the

early Middle Pleistocene, it was also frequented by a

variety of carnivores during the same period. Despite a

surrounding environment only sparsely tree-covered, an-

abundant mammal fauna was present in the area and this

favoured th e subsistence of both hominids and carnivor es.

The semi-arid conditions of the time were responsible for

Figure 1. Location map and position of the main Lower Palaeolithic sites excavated at Casablanca (A). 1, Sidi Abderrahmane

Grande Exploitation. 2, Sidi Abderrahmane-Cunette with Cap Chatelier and Bears Cave. 3, Sidi Abderrahmane-Extension. 4,

STIC Quarry. 5, Thomas Quarry I. 6, Thomas III Cave . 7, Thomas III “fissures”. 8, Oulad Hamida 1 (Rhinocer os Cave ).

R. GALLOTTI ET AL. 375

Figure 2. General view of the Thomas I Quarry.

the complex sedimentation and post-depositional proc-

esses present in the cave. Absolute dates place strati-

graphic Unit 4 between 360 and 470 kya, but more re-

cently, this has been pushed towards 500 kya by laser

ablation ICP-MS. Nevertheless, bio-stratigraphy and

litho-stratigraphy point toward s an even greater antiquity

[20].

Middle Pleistocene levels also occur in the Oulad

Hamida 1 Quarry, where Rhinoceros Cave has yielded a

rich collection of micro and macro mammals with re-

markably abundant remains of white rhinoceros, associ-

ated with a rich Acheulian lithic assemblage (Figure 3)

[19].

3. The Application

These sites, extensively excavated, yielded an enormous

quantity of lithic objects and faunal remains. Due both to

the extent of the investigated areas and the number of

finds, technological tools for recording spatial data were

found necessary during the excavation phases but more

importantly for intra-site spatial analyses undertaken to

elaborate on the locational information associated with

the finds. To manage the huge quantity o f data a GIS was

chosen because of its almost limitless possibilities for

recording alphanumerical and graphical data, of visuali-

zation, analysis and subsequent processing. We used two

GIS software products to perform different types of spa-

tial analyses. The logical structure of our methodology is

summarized in Figure 4.

3.1. Recording Archaeological Evidence

Documentation for the excavations at Thomas I and Ou-

lad Hamida 1 Quarries exists in two different forms: pa-

per archives recorded before the use of an electronic ap-

plication (2006) and data collected using an electronic

Figure 3. Top: General view of the Rhinoceros cave. Bottom:

Detail of the excavation.

information system. The amalgamation of these data was

necessary to create an information resource which could

be manipulated to manage all the classes of data simul-

taneously. The paper documentation consisted of a writ-

ten catalogue of the finds from the excavations accom-

panied by the relative plans. Th e first step was to co nvert

the written alpha-numerical data (the catalogue entry for

each lithic artifact or bone) to digital format. Microsoft

Access was used to create the alpha-numerical archives

(and is also used to collate new information). It was

chosen mainly for its simplicity of use in the creation of

tables and templates and especially because it permits the

use of personalized dictionaries, thus facilitating data

entry and assuring, at the same time, the homogeneity of

the archived data in its new form.

After the conversion of the paper alpha-numeric ar-

chives, we computerized the existing paper maps that

had been made for every square meter of the excavated

areas. The excavations were carried out within a grid of 1

× 1 metre squares, within which every single find had

been accurately positioned.

R. GALLOTTI ET AL.

376

Figure 4. Conceptual scheme of the informatics application.

This grid was imported into MapInfo Professional,

referenced on non-terrestrial coordinates using a metric

scale and then translated into a vector format. We created

two local networks: one for Thomas I Quarry, including

Unit L and Hominid Cave (Figure 5), another for Rhi-

noceros Cave. Every paper map was scanned, imported

into MapInfo as a raster image and located in its proper

place in the appropriate local network using the coordi-

nates of the vertices of the corresponding squares.

Any object contained within the image was drawn as a

polygon and linked to the database through its inventory

number which is a unique key. It is also possible to view

any found object as a point thanks to the MapInfo Ex-

tract Coordinates utility, which can au tomatically extract

the x and y coordinates of the midpoint of a polygon.

The second step was to create an appropriate system

with which to record newly generated excavation data.

We chose a flexible structure using Total Station inte-

grated wi t h orthophotos.

Usually, we use Total Station to record point data of

archaeological objects on maps collating this type of

information. If the excavated area is particularly repre-

sentative in some way or portrays archaeological objects

of large dimension s, we utilize the orthophotos to record

such finds as polygons. We take a photo of each square

metre of the excavation and use RDF software to trans-

form it into an orthophoto. As with the documen tation of

earlier excavations, the orthophoto is imported into

MapInfo Professional, referenced, translated into a vec-

tor format and then every graphical object depicted is

linked to the database through its inventory number.

3.2. Processing of Spatial Variables

Both alphanumerical and graphic data are managed by

GIS software. MapInfo Professional is the principal

software used to elaborate thematic maps and sections

and frequency matrixes. Another principal software used

to elaborate thematic maps and sections and frequency

matrixes. Another GIS product, ArcView, was added to

our suite because of its capabilities in processing density

analyses. Combining alpha-numeric and graphic infor-

mation makes it possible to present diverse queries to the

database and to interrogate simultaneously the al-

pha-numerical data with its corresponding graphic ob-

jects. The results thus created are then saved as new ta-

bles and maps. It is thus possible to generate numerous

thematic ‘maps’ that present the object categories found

in the excavation, as unique categories as well as show-

ing their association with other selected categories or

types of information, thus allowing spatial comparisons

to be made between any number and variety of different

objects and/or data (Figure 6).

The huge number of finds discovered in the three sites

concerned makes it difficult to obtain accurate impres-

sions of their spatial distribution in any normal concep-

tual manner; so the topological features of GIS are used

to create maps derived from the data and present it as

R. GALLOTTI ET AL. 377

Figure 5. Local network with excavated areas at Thomas I Quarry.

frequency analyses, or to obtain density values and to

schematize the distribution trends (concentrations or

dispersals) of artifacts.

For maps recording frequencies, finds were grouped

and counted per square [13] using an SQL procedure

based on the topological overlay of the 1 m by 1 m ex-

cavation grid for each thematic level. This procedure

allows automatic calculation of the number of objects

whose central point falls within each square. The maps

thus obtained contain the total number of each category

of finds falling within each grid square. Frequencies in

these maps are expressed by ranges of standard values

delineated by ‘natural breaks’, a method that identifies

the break points by picking the position within each class

that best groups together similar values and maximizes

the differences between classes. The features are thus

divided into classes whose boundaries are set at the posi-

tion where a relatively big jump in the data value occurs

(Figure 7). By combining two or more frequency ma-

trixes, it is possible to compare the frequency of each

category per square metre and present the result graphi-

cally (Figure 8). To provide a rendering of object con-

centrations not linked to the spatial units defined by the

excavation grid, density maps were created. Points cor-

responding to the centroid position of each object were

exported into ArcView, where density plans were gener-

ated using Spatial Analyst. The density function calcu-

lates the number of points in a level over a continuous

surface. Thus, the occurrence and proximity of points is

highlighted through the generation of a new map of den-

R. GALLOTTI ET AL.

378

Figure 6. Thomas I Quarry—Hominid Cave, Locus 2. Thematic map of all remains.

sity values beginning from a given point. Values are ex-

pressed through density curves quantified on the basis of

a k-nearest neighbour distance that is smoothed using

Kernel Density Estimation (a fundamental data smooth-

ing operation where inferences about the population are

made, based on a finite data sample) (Figure 9).

The vertical distribution of finds is projected on lon-

gitudinal and transverse cross-sections which generally

correspond to a two-dimensional representation: by

ranging the values of x or y respectively on the abscissa,

and those of z on the ordinate, it is possible to plot the

projection of all finds and thus map these kinds of

cross-sections. This expedient is necessary because the

GIS packages lack 3D topology and consider z values as

attributes rather than as true spatial coordinates (Figure

10).

R. GALLOTTI ET AL. 379

Figure 7. Thomas I Quarry—Unit L. Frequency matrixes per square meter of all remains.

Figure 8. Thomas I Quarry—Unit L. Relationship among the frequencies of different categories of finds per square meter.

4. Conclusions

Systematic stratigraphic excavations, documented with

three-dimensional recording, and the use of intra-site

spatial analyses using GIS and associated systems proved

invaluable tools for analyzing the Acheulian sites at

Casablanca which are characterized by an extremely high

number of finds and by complex post-depositional

mechanisms. The integrated approach that we used per-

mitted us to record, follow and analyze each phase of the

research, from the first stage of recording information to

the later step of data interpretation. Our use of the sys-

tems mentioned allowed a more immediate management

of the data related to the spatial interrelations of fossils,

artifacts and geology through continuous evaluation of

all the attributes of distribution and analysis available in

R. GALLOTTI ET AL.

380

Figure 9. Thomas I Quarry – Unit L. Density map of all remains.

Figure 10. Oulad Hamida 1—Rhinoceros Cave. Excavation 2009. S-N cross-section with the projection of all remains.

the various programs.

This model for handling large amounts of information

simultaneously has clear potential for storing and orga-

nizing the huge volumes of data generated by any exca-

vation and for illuminating and unraveling the complex

processes responsible for the formation of Palaeolithic

sites. The model developed for the Casablanca sites can

be broadly appli e d t o other si milar sites.

5. Acknowledgements

The authors thank anonymous readers whose comments

allowed us to improve this paper and Peter Bindon for

the revision of the English language. Excavations take

R. GALLOTTI ET AL.381

place within the frame of the Programme Casablanca of

the Institut National des Sciences de l’Archéologie et du

Patrimoine and are funded by Ministère de la Culture of

Morocco, Ministère des Affaires étrangères et eu-

ropéennes of France, Région Aquitaine and the Depart-

ment of Human Evolution of Max Planck Institute for

Evoluti onary Ant hropology at Leipzig.

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