To continue our discussion about
Fort Hunter data collection, processing and usage we will take a look at one of
the most important factors in understanding and preserving an archaeological
site. This factor, as is commonly stated in the real estate industry is,
“location, location, location”. In order for archaeologists to understand the
landscape of an archaeological site we must know where everything is in
location to one another both horizontally and vertically. The reason it is so
important to record the location of artifacts, features and structures, is that
once they are removed from the ground there is no way put them back in their
exact place again. In addition, maps depicting the exact location of different
types of artifacts are necessary to identify artifact patterning and activity
areas. The excavation methods employed by trained archaeologists insure that
the entire archaeological record of a site is properly recorded during excavation
as archaeology is a destructive science.
In order to preserve this
locational information, sites such as Fort Hunter, are excavated based on a
grid set from our datum (a known fixed point). This allows archaeologists to go
back to a site, whether it is from year to year or twenty years from now, and
re-establish the grid. With good documentation and a re-established grid,
archaeologists can determine what areas had been previously excavated. The grid
also provides the horizontal locational information of artifacts and features
that have been removed from that area. At Fort Hunter our grid is in 5 by 5 foot
square increments, which is termed as a unit. We name our units using the
northing and easting (for example N90E10) of the southwest corner of a square. This
designation allows us to easily reference that unit and keep track of the
artifacts or features.
Overview of Fort Hunter excavations with stakes and string
line indicating the grid, Fort Hunter 2007
Once a grid is established, we
begin excavating units in levels in either arbitrary levels of a predetermined
measurement (for example 3 inches or 5 centimeters etc.) or based on soil
layers, which are indicated by changes in soil color and texture. The layers
are often given an alpha designation based on the soil type. Identifying the
same types of soil throughout the grid allows us to see how the soil layers
slope and change over the landscape. These anomalies can indicate different
geologic/climatic processes as well as point to the activities of people on the
landscape. Within these natural layers, we then excavate in arbitrary levels. These
levels and layers are measured below the set datum elevation, which provides
the vertical location information of the artifacts found within that level.
As mentioned in our last blog, “…unique
catalog numbers are assigned to each provenience.” The provenience mentioned
here is the locational identity of the artifacts based on the horizontal and
vertical measurements discussed above. It is with the locational information
and the well-developed catalog that we are able to know how the artifacts and
features are related to one another.
Now that we have explained how we
use the grid, we can look at how we layout the grid, take measurements and how
we manipulate the data in the lab. The basic idea of establishing a grid is to
create accurate 90 degree angle squares and in order to do this archaeologists
use a transit, tape measures and some basic geometry. A transit is an instrument
that sights straight lines and different angles. The transit is also used with
a stadia rod to measure the depth of a level.
Staff member using transit, just beginning to set up grid,
Fort Hunter 2010
Today we use a newer technology
called a total station. A total station is an electronic transit which can also
sight straight lines and angles as well as use a laser and prism to collect
precise horizontal and vertical measurements of a point on our grid. Using the
Top Con Data Collector (handheld attachment to the total station), we are able
to easily store and look up point information while in the field and also
download and convert the data into a spreadsheet format.
Staff member using Top Con total station, Fort Hunter 2014
Staff member holding prism to take measurements using total
station, Fort Hunter 2014
Example of collected data in spreadsheet format
With the data collected, we are
able to then create useful maps, which allow us to analyze the relationship
between features, structures and artifacts. It is also possible to use unit and
artifact data to create distribution maps. Common programs used to create such
maps include Golden Software’s Surfer and Autodesk’s AutoCAD.
Example of a feature map, showing relationship of several
different features
Example of an artifact distribution map
Example of a profile map
With today’s technology, and the
detailed information we collect, there are many different mapping options
including those above as well as the ability of creating 3-D images. Knowing
the relationship of artifacts and features on the landscape provides the
foundation that archaeologists use to develop explanations for how past humans
were living on and using the landscape. Creating these maps provides a useful
visual comparison of how features, artifacts and structures are placed on the
landscape. Finally, maps also provide a great way to interpret an
archaeological site and how we present different ideas of the past to others.
We wanted to take a moment to
remember a longtime volunteer, Sheila Dunn. Sheila was a dedicated volunteer
who put a lot of time and effort into collecting data and creating Fort Hunter
maps for us. Using her training and past experience in watershed surveys she
was always ready and willing to help out in any way and put in great effort to
create some of our first maps of the Fort Hunter excavations. Thank you,
Sheila.
Sheila Dunn
We hope to see you all in the new
year at the 100th anniversary of the Pennsylvania Farm Show running
from January 9-January 16, 2016. Look for us in a new location this year
directly off of the Maclay Street entrance near the children’s carousel. From
all of us in the Section of Archaeology at The State Museum of Pennsylvania -
Have a happy and safe holiday!
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