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Using GIS to Explore Legacy Spatial Data at Isthmia

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Abstract

As is the case at many excavations that had their start before the "digital revolution, " the Ohio State University Excavations at Isthmia must face the challenge of updating its traditional paper-based recording systems in order to take advantage of the many digital tools that are available for archaeological data analysis. This is most clearly illustrated in the case of Geographic Information Systems (GIS), which combine digital databases with scalable electronic maps to enable statistically significant visual analyses of the types of complex datasets common to archaeological sites. In order to serve as an effective tool for archaeological analysis, a GIS must rely on precisely mapped features in combination with archaeological evidence in electronic form. Yet at Isthmia, these forms of information are "locked up" in handwritten notes and drawings contained in a variety of notebooks, maps and plans. This poster outlines the process by which that analog information is being made digitally accessible and therefore useful for spatial analysis.
Using GIS to Explore Legacy Spatial Data at Isthmia
Louise M. Steele1 and Jon M. Frey, Ph.D2
1Department of Anthropology, Michigan State University
2Department of Art, Art History, and Design, Michigan State Univeristy
As is the case at many excavations that had their start before the “digital revolution,” the Ohio State University Excavations at Isthmia must face the challenge of updating its traditional paper-based
recording systems in order to take advantage of the many digital tools that are available for archaeological data analysis. is is most clearly illustrated in the case of Geographic Information Systems
(GIS), which combine digital databases with scalable electronic maps to enable statistically signicant visual analyses of the types of complex datasets common to archaeological sites. In order to
serve as an eective tool for archaeological analysis, a GIS must rely on precisely mapped features in combination with archaeological evidence in electronic form. Yet at Isthmia, these forms of in-
formation are “locked up” in handwritten notes and drawings contained in a variety of notebooks, maps and plans. is poster outlines the process by which that analog information is being made
digitally acessible and therefore useful for spatial analysis.
Having succeeded in creating a unied digital basemap of the site, it became possible to
focus on the associated problem of locating catalogued artifacts in and around the sanc-
tuary. Lacking a systematic grid system for their site, archaeologists at Isthmia have tra-
ditionally relied upon locally generated plans to map the locations of objects and features
uncovered in excavations. ese plans, which are accompanied by an informal grid sys-
tem, appear in the opening pages of most eld journals and are referenced throughout
the discussion that follows. Of course, these sketch plans dier in quality from journal to
journal and lack the overall accuracy of an actual state plan -- a factor that must be ad-
dressed when attempting to generate reliable data for statistically signicant spatial data.
Actual references to the ndspots of objects in the eld journals are of two types. Occa-
sionally, for artifacts understood to be important at the moment of discovery, excavators
provided coordinates referring to a specic plan in that eld journal. More commonly,
objects recognized as signicant at a later stage in the cleaning and recording process are
simply associated with a stratagraphic unit. While this was not always the case, in both
scenarios, the nal catalogue number of the object is supposed to be wrtiten into the eld
journal as a part of the cataloging process. us, as a rst step, researchers are focusing on
identifying all references to catalogued artifacts in the excavation journals, then estimat-
ing each objects place of discovery, in order to create the rst overall plan of artifact scat-
e Problem
is project builds on the work initiated last sea-
son to create a unied, scalable, digital model of
the Sanctuary of Poseidon at Isthmia. Previous-
ly, features at the site were represented in a num-
ber of actual state plans and less accurate overall
site plans that could not be directly related to one
another. Moreover, even the most accurate plans
were created using an outdated projection sys-
tem and datum that could not be easily related to
GPS data collected in a more universally relatable
sytem. is shortcoming was remedied by means
of an intensive aerial survey that produced a centi-
meter accurate, geospatially referenced orthomo-
saic of the site, which could serve as a base map
onto which all prior plans of the sanctuary and its
larger regional setting could be projected.
Georeferencing the Plans Adding the Sketches
Plotting the Points
In the rst stage, digitized copies of hand-drawn actual state plans are
modied to achieve a “best t” with the newly created orthophoto mo-
saic of the site. Notice the small distortions in the semi-transparent state
plan.
Next, these plans as well as the real world features that remain visi-
ble since the time of excavation are used to geospatially reference the
sketches of excvated trenches with their sketch-specic coordinate
systems.
Finally, artufacts that have been located according to sketch-specic
coordinate systems are plotted into the GIS. Note the systematic use of a
naming convention, which oen must be imposed on inconsistent data.
Preliminary Results
ere can be no doubt that this is a very time-consuming process. In order to include the
greatest amount of detail, information about each artifact must be aggregated from a vari-
ety of sources. Evidence concerning objects rst discussed in a eld journal is augmented
with details written onto the catalogue cards and ocasionally artifact drawings, photo-
graphs or other forms of process metadata. is would suggest that, into the near future,
few aspects of this workow will be able to be automated.At the same time, even though
this project is only in its preliminary stages, the results are already promising.
A comparison of the location of coins that have been assigned a data reveals:
e eastern and southwestern parts of the ortications exhibit a fairly uniform distri-
bution of artifacts
In the area of Tower 15, Byzantine (6th-13th c AD) coinage far outnumbers that of other
artifacts. unlike the eastern and southwestern parts of the fortications, which exhibit a
generally uniform distribution of artifacts
In the area of Tower 14, Frankish (13-15th c AD) and Venetian (14th-16th c AD) coins
are more commonly found, especially in the area of a one-room building appended to
the western face of the Byzantine fortication.
Figs. 4 and 5: Comparison of the Tower 14/Tower 15
ara on the west side of the Fortress(le) with the Tower
8/ Tower 9/ Tower 10 area on the south (right). Note
the concentration of the predominately Byzantine coins
near Tower 15 and the concentration of Venetian and
Frankish coins near Tower 14. is periodization is not
seen, however, in the Tower 10 area.
Because all information from previous decades
was documented on paper, data about the objects
themselves must also be converted to electron-
ic format. As is the case when plotting the spatial
data, this step in the process is also done manu-
ally. In this case though, the Isthmia Excavation
makes use of its installation of the Archaeological
Resource Cataloging System (ARCS), to organize
an online, crowd sourced eort to transcribe the
essential details about each object from digitized
copies of original inventory catalogue cards. Once
this stage is complete, information can be export-
ed from ARCS in a format that is easily integrated
into the sites GIS.
Figure 6: Screen caputre of the data transcription tool in the Isthmia ARCS
Next Stages
Because recording inventoried objects in the midst
of an active eld season was a haphazard process,
references to many artifacts did not nd their way
back into notebooks. us, it will be important to
examine all inventoried object cards to extract any
geospatially signifcant evidence that has not yet
been recognized.
Because the locations of some artifacts were de-
scribed with greater precision than others, it will
be necessary to develop a more eective way to
indicate visually a relative degree of condence in
the locations that make up the artifact scatters on
the plan. What is the best way to represent the lo-
cation of an artifact that can only be identied as
part of a stratigraphic unit?
Because some excavators were more careful to re-
cord any artifact of potential signicance, the re-
sulting plots of objects may be less an indication of
actual artifact densities than individual practices of
collection and recording. It may be worthwhile to
adopt techniques developed among survey archae-
ologists to address inter-observer error.
Because most GIS systems only oer a two-di-
mensional approximation of a three-dimension-
al reality, it is important to consider how to best
represent stratigraphic layers in examining spatial
relationships. At present, the scatter of artifacts
across the site is potentially misleading, as it fails
to distinguish between areas that were truly more
artifact-rich” and areas that were simply excavated
more deeply through more strata of human activi-
ty.
Much remains to be done with other eld journals both in the area of the Fortress as
well as other more systematically excavated areas of the site. Yet already, this project
has identied the following items in need of more attention:
Acknowledgements
is project could not have been possible without the support of the following individuals and organiza-
tions:
• Timothy E. Gregory, Director of the Ohio State University Excavations at Isthmia
• Betsy Gebhard, Director of the University of Chicago Excavations at Isthmia
• James Herbst, Architect, American School of Classical Studies at Athens Excavations at Corinth
• Amanda Tickner, GIS Librarian, MSU Libraries
• MATRIX Center for Digital Humanities and Social Sciences
• MSU College of Arts and Letters Undergraduate Research Initative
I would also like to thank Dr. Frey for his mentorship and advising during this project.
e Process Artifact Data
Contact Information:
steelelo@msu.edu
louisemsteele.com
Figure 1: (Le) Field journal with informal grid system; Figure 2: (Center) Field journal with artifact location and catalogue number
Figure 3: (Right) Plan of the Tower 14 region of the Fortress at Ithmia
Figure 7: Mosaic of all eld journal sketches in the Tower 14 area of
the Fortress at Isthmia
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