By: Jennifer L. Groves, Karen A. Borstad, & Gary L. Christopherson
The University of Arizona
The Annual Meeting of the
American Schools of Oriental Research
A new surface survey project was launched at Tall Jalul, Jordan, during the 1994 field season. While surface surveys are not new to archaeology, the methodology and techniques implemented in this project were unique. The research was designed to explore the relationship between surface sherds and subsurface archaeological material remains. Utilizing a site-wide grid system of six by six meter squares, elevation data and pottery were systematically gathered. Analysis of these data was carried out within a geographic information system. This spatial database was used to document the distribution of surface sherds by period and form at Tall Jalul and to produce topographical maps and ceramic distribution maps.
In the context of ancient Near Eastern talls, the relationship between surface sherds and subsurface archaeological material remains uncertain at best. Do sherds scattered across the surface of an ancient mound reveal to the excavator such things as residence patterns, population fluctuations, and social differentiation, or are they just scattered bits of pottery? During the summer of 1994, the Madaba Plains Project (MPP) began a long-term investigation of this question using surface sherds collected from Tall Jalul, Jordan. This investigation differed from most surface surveys in its utilization of geographic information system (GIS) technology in the analysis of the data collected, with particular emphasis on spatial distribution. Although final results will not be available for several years, this preliminary report discusses the methodology of the project and provides some preliminary results.
Tall Jalul is located on the Madaba Plain at Palestine Grid coordinates 231200 E, 125400 N, ca. 16.5 kilometers south of Tall al-Umayri, near the Amman-Madaba road. Albright and Glueck both visited the site during the 1930's, describing Jalul as "a large mound commanding the surrounding plains and visible for considerable distances around" (Glueck, 1934). Jalul was first investigated by The Madaba Plains Project in 1974, when it was visited by Robert Ibach and the Hesban Regional Survey (Ibach, 1976; Ibach, 1987). The Hesban team returned for three weeks in 1976 to conduct an intensive surface survey of the Tall (Ibach, 1978b). During this time, they collected 26,225 sherds from 101 randomly located 10 x 10 m squares. Of these sherds, 2000 diagnostics were read by James Sauer, with the majority belonging to the Iron Age I and Iron Age II periods. The Madaba Plains Project returned to Jalul in 1992, with excavations directed by Randy Younker. With three field seasons (1992, 94, 96) completed, the excavation at Jalul has opened four fields, uncovering extensive late Iron II remains (Herr, Geraty, LaBianca, & Younker, 1994; Younker, Geraty, Herr, LaBianca, & Clark, 1996).
For the 1994 surface survey, systematic collection of ceramic and elevation data from the surface of Tall Jalul utilized the excavation grid. Coordinates for this grid were based on the Palestine Grid coordinate system which uses the meter as its standard unit of measure. The Tall Jalul excavation grid covers an area of 8.91 hectares, contained within the following coordinates: Minimum X = 231034 meters East, Minimum Y = 125242 meters North, Maximum X = 2231364 meters East, Maximum Y = 125512 meters North. The excavation grid divides this area into 45 rows and 55 columns, creating 2475 six by six meter data collection squares. For this study, each collection square was referenced by its row and column numbers. Thus, the first square, beginning in the NW corner of the Tall, was referenced as 0, 0, and the last as 44, 54. In addition, a unique identification number (ID) was assigned to each square, permitting the transfer of data between related database files. This grid can be seen in Figure 1, where a red cross appears at the center of each collection square.
To facilitate data collection in the field, the squares were bound into larger units called groups. These groups measured 60 X 60 meters and contained 100 squares. Each day a single group was processed. Though arbitrary, the group designations were helpful in the field, providing a convenient reference to a general area of the Tall, acting as anchors for laying out collection squares, and serving as a natural goal for each day's collection.
The first step in the field was to locate the four corners of the group scheduled for collection. Once these corners were located, a 100 m tape was used to establish its outer boundary. The tape was held taut between two corners while workers placed survey flags every 6 meters. Using these flags as a guide, the tape was then stretched across the group and flags were again placed every six meters, creating a grid of 100 data collection squares.
Once the collection squares had been delineated by survey flags, data collection began. Two types of data, elevation and ceramic, were collected from the squares. A theodolite was used to gather elevation data for each square. The stadia rod was placed at the center point of each square, sighted by the surveyor, and recorded on a simple recording sheet. At the same time, plastic bags with pre-written ID tags were placed in the center of every other square, checkerboard fashion. Volunteers then collected all surface sherds from the designated squares. At the end of the season, the pottery was transferred to a ship at Aqaba. It arrived in Los Angeles 5 months later and made its way to Tucson, Arizona in December, 1994.
Once in Tucson, the pottery was processed and recorded on paper forms. As each bag was opened, a new recording form was filled out with identification information from the enclosed tag. The pottery was counted, and weighed by form and period and the numbers entered on the forms. Diagnostic sherds were saved, either as part of a comparative collection or returned to their plastic bags to await shipment to the Horn Archaeological Museum at Andrews University.
The data was entered into three separate digital database files, one for elevation data and two for ceramic data. Initial data entry was done on a portable PC using FoxPro software (Microsoft Corporation, 1993). The elevation data from each square was entered as a record, with its associated square ID number and the row and column numbers from the collection grid. Ceramic data was entered into a master file of square identification information, and a related detail file of the pottery readings. These data were then transferred to ARC/INFO (ESRI, 1995), a GIS running on a SUN workstation computer, where they were processed interactively in the INFO subsystem in order to validate the data and correct errors.
Although final results from this project require excavated data which will not be available for several years, preliminary products from this survey demonstrate its efficacy. These products fall into two categories: summary statistics based on the ceramics collected, and maps detailing elevation and ceramic distribution at Tall Jalul. The remainder of this paper will discuss each product in turn.
In all, 43,199 sherds, with a total weight of just under 623 kilos, were collected from the surface of Tall Jalul. Of these, 2791 were diagnostic, more than half of which were Iron II sherds. When compared to Ibach's collection from 1976 (Figure 2), some significant differences appear, most notably the disparity between the Iron I and Iron II samples, but also the much smaller quantity of LB pottery from the 1994 collection. These disparities are likely the result of the 1976 survey removing much of the earlier material. Buried by the Iron Age II city, Iron Age I and Bronze Age materials would presumably reappear at a slower rate. This situation presents a unique opportunity to make comparisons. Once the 1976 data has been incorporated into our databases, spatial analysis of the two surveys may give insight into the processes by which sherds are transported to the surface.
Because they are spatially referenced, the elevation and ceramic data in the database can be used by a geographic information system to make maps. Maps created for this study can be divided into two groups, elevation maps and ceramic distribution maps.
Before discussing the creation of these maps, it is necessary to understand something of the nature of geographic information systems. GIS data comes in two basic types, vector and raster, both of which were utilized by this project. Vector maps look much like traditional paper maps, in that they are composed of points, lines, and polygons. Unlike paper maps, however, vector elements in a GIS are typically connected to powerful databases, which allow data to be related to these elements. This allows the archaeologist to manipulate map data based on standard database queries. For instance, it is possible to query the database to create a map displaying only those collection squares where Iron II bowls were found (Figure 3)
Raster data is stored in a spreadsheet like format of columns and rows which correspond to X and Y coordinates in the real world. The intersection of each row and column is known as a cell, and each cell in the raster contains a Z value, or number, which can represent anything from elevation, to archaeological sites, to soil types. As such, raster maps are ideal for modeling continuous surfaces, such as elevation in a region, or pottery distribution across the surface of a tall. (Additional discussion of GIS and the utility of GIS for archaeology can be found in a number of books and articles, including Allen, Green, & Zubrow, 1990; Burrough, 1986; Christopherson, 1996; Kvamme, 1989; Kvamme, 1992; Lock & Stancic, 1995).
The first products created were two elevation maps of Tall Jalul. The first of these was a digital elevation model, or DEM. DEM's are created by algorithms which determine elevation values for all cells in a raster grid by interpolating them from known elevations. As already noted, one type of data collected during the survey was an elevation datum for each collection square in the grid. To create a DEM of Tall Jalul, a raster consisting of 2 X 2 meter cells was created for the project area. Elevation values for each of the 22,275 cells in this raster were interpolated in ARC/INFO from the 2475 elevation values collected at Tall Jalul. This process produced the DEM in Figure 4. In this map, the blues are low values, and the yellows are high values, making it easy to discern such features as Tall Jalul's western acropolis and the presumed water system located in the large depression near the eastern edge of the Tall. These features become even clearer when the DEM is viewed as a 3-D model. In Figure 5, the DEM of Tall Jalul is modeled in 3-D, and rotated to show the Tall from four different perspectives.
A more traditional topographic map was also created. Produced in much the same way that a surveyor would record elevation points and then interpolate contours from the points, the contours in this map were interpolated by ARC/INFO from the 22,275 elevation points in the DEM. Text, legend, and the other elements were then added to the map (Figure 6), which was plotted at a scale of 1:500 on an HP750C ink plotter. A smaller, encapsulated postscript (EPS) version of this map was also created for use in publications.
In addition to elevation products, a number of maps were created detailing ceramic distribution across the surface of Tall Jalul. These maps were built in much the same way as the DEM. Again a raster of 2 X 2 meter cells was imposed on the surface of the project area; however, instead of using elevation values, pottery counts and weights were used to interpolate the surfaces. A program to facilitate this process was written in ARC/INFO's programming language to work within the GIS. Upon starting the program, a pop-up menu appeared which allowed the user to select ceramics by period and form. For example, if the researcher was interested in Iron Age II bowls, the program would query the pottery database for that period and form, creating a new vector map with point locations for those squares where Iron Age II bowls were found. Based on this point map, raster maps were generated for Iron II bowls, by count and by weight. Figure 7 shows the distribution of Iron II bowls by weight across the surface of Tall Jalul. Again blues are low values and yellows are high values. Contour lines and the location points for Iron II bowls were included to help place the distribution within the context of Tall Jalul. (A more technical discussion of the procedures used to create these maps can be found by following this link.)
As with the DEM, these raster surfaces can also be displayed as three dimensional models. Figure 8 illustrates the distribution of Iron II bowls, this time with the weight shown in three dimensions. Another type of 3-D display can be created by draping the pottery distribution map across the surface of the Tall Jalul DEM (Figure 9). This type of map allows excellent visualization of pottery distribution across the surface of the site.
Ultimately, these ceramic distribution maps must function as more than just pretty pictures. Although the analysis phase of the project has only just begun, a few preliminary observations are possible. First, there are differences between maps based on weights and maps based on counts for the same form and period. An example of these differences can be seen in Figure 10, where maps for the distribution of Iron Age II kraters, by weight and by count, are shown. In Figure 11, these distributions are again shown, but in 3-D where differences between counts and weights are more striking. Given the emphasis placed on ceramics in Levantine archaeology, these differences are important. For example, a regional survey could arrive at different conclusions concerning settlement patterns depending on whether counts or weights were used to determine spatial relationships.
Second, it is possible to create maps that illustrate changing spaital/quantitative distributions of surface ceramics. Figure 12 presents changes in these distributions from EB to MB and from Iron Age I to Iron Age II. Differences between periods are even more pronounced when displayed as 3-D models (Figure 13). With only three excavation seasons completed, ceramic evidence from stratigraphic contexts at Tall Jalul is limited, and it is too early to say whether there is any correlation between the fluctuations seen in these maps and the site's settlement history; however, given the results of previous excavations and hinterland surveys in the Madaba Plains region (Boling, 1989; Christopherson, forthcoming, 1997a; Christopherson, forthcoming, 1997b; Geraty, Herr, LaBianca, & Younker, 1989; Geraty, Herr, LaBianca, & Younker, 1991; Ibach, 1976; Ibach, 1978a; Ibach, 1978b; Ibach, 1987; LaBianca, 1990; LaBianca, Herr, Younker, Geraty, Clark, Christopherson, et al., 1995; Younker, 1991; Younker, et al., 1996), these fluctuations were not unexpected.
Finally, and most unexpectedly, there may be some correlation between surface and sub-surface distributions of pottery. Remembering that excavated strata have not yet reached Iron Age I levels, there may be a correlation between collar rim storejars and the city walls at Tall Jalul. This distinctive pottery form was one of the first for which a distribution map was made. Distribution for this pottery type forms a rather distinct pattern, with a ring of high values surrounding an area of low values. If we put this in the context of Tall Jalul it becomes clear that this ring corresponds with the slopes of Jalul (Figure 14). The importance of this is best understood in the context of excavated sites with significant quantities of these vessels. There were large quantities of collar rim jars at Tall al-Umayri. At Umayri, collar-rim storejars were found in concentrations within the casemate wall which encircled the top of the mound. If we look again at the distribution of Iron I storejars from the surface of Tall Jalul, there seems to be a similar pattern (Figure 15). (It should be pointed out that most pottery forms generally had heavier concentrations around the edge of the Tall, but with Iron Age I storejars the concentrations were exclusively around the edge. Confirmation of this pattern awaits future excavation seasons.)
Although answers to the questions that prompted the Tall Jalul surface survey depend on future excavation seasons, data already collected has provided preliminary results. The project has collected a baseline of ceramic data, against which excavated materials can be compared. It has also produced elevation maps which are already in use by the project. New maps can be made each season to reflect the ongoing excavation at Tall Jalul. Ceramic distribution maps have been created and can be used in planning the location of future excavation fields at Tall Jalul. As excavation continues, the surface survey project will focus on two questions. First, does the distribution of surface sherds accurately predict social differentiation or the boundaries of specific use areas, such as domestic, administrative and industrial sectors? and second, to what extent does the distribution and quantity of surface ceramics correlate with excavated remains at Tall Jalul?
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The authors would like to thanks the excavators of Tall Jalul, especially
the director, Randy Younker, whose support made this project possible; the
field supervisors who supplied us with volunteers each day; the surveyors,
Valentin Gligorov and Mark Ziese, who very patiently took 2475 elevation
points; the volunteers who collected the pottery each day; and Laura Mazow,
who served as quantitative engineer in Tucson. We also want to thank the
Advanced Resource Technology lab at the University of Arizona for access
to computer hardware and software.
Jennifer L. Groves is a graduate student in the Near East Studies Department at The University of Arizona. She has been involved with the Madaba Plains Project since 1989, where she is a Field Supervisor with the Tell Jalul Excavation. Correspondence may be sent to: Near East Studies Department, The University of Arizona, Tucson, AZ, 85721, or by email: Jennifer Groves -- jgroves@U.arizona.edu
Karen A. Borstad is a graduate student in the Near East Studies Department, and a Research Assistant in the Advanced Resource Technology Group at at the University of Arizona. She has been involved with the Madaba Plains Project since 1994. Her primary responsibilities are programming and maintaining the excavation database. Correspondence may be sent to: ART Group (SRNR), 203 Biological Sciences East, The University of Arizona, Tucson, AZ, 85721, phone (520) 621-3045, or by email: Karen Borstad -- email@example.com
Gary L. Christopherson is a Ph.D. candidate in the Near East Studies Department, and a Research Assistant in the Advanced Resource Technology Group at The University of Arizona. He has been associated with the Madaba Plains Project since 1987, where he is a Field Director in charge of archaeological survey. Correspondence may be sent to: ART Group (SRNR), 203 Biological Sciences East, The University of Arizona, Tucson, AZ, 85721, phone (520) 621-3045, or by email: Gary Christopherson -- firstname.lastname@example.org