The Fiske Center Blog

Weblog for the Fiske Center for Archaeological Research at the University of Massachusetts Boston.

Further Research: The Buildings on Burial Hill, part 1

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Georeferencing

This post is part of the Further Research series (see here for an explanation).

During the 2014 excavations on Burial Hill in Plymouth, we uncovered the foundations of two historic buildings and deposits from two additional building lots. One of our questions that needed follow up research was which buildings these were: who owned them and what were they used for? There are maps from 1874 and 1885 that show the buildings along this stretch, but tying the historic maps to the modern landscape is not always a straightforward task.

A section of the 1874 Beers map of Plymouth showing the buildings along School Street.

A section of the 1874 Beers map of Plymouth showing the buildings along School Street.

A section of the 1885 Sanborn map showing buildings on School Street.  Note that some buildings have been demolished since the 1874 map and others have been reconfigured.

A section of the 1885 Sanborn map showing buildings on School Street. Note that some buildings have been demolished since the 1874 map and others have been reconfigured.

The process of using GIS to place a historic map on the modern landscape is called georeferencing. To do this, you need points on the historic map that still exist on the modern landscape. In an urban area such a Plymouth, this is a challenge because there have been a number of episodes of urban redevelopment that have moved streets, reshaped the coastline and streams, and demolished or moved historic buildings. All of the buildings along School Street, our study area, for example, had been demolished since the maps were made. We found two points near our study area that seemed to be stable: the corner of a historic church and of the old jail. Both of these buildings exist on the maps and in the modern world, so we could go and take GPS points on corners of the buildings and use those points to relate the maps and the modern landscape. Using these two points, we georeferenced the maps. (Since we did this, the old jail on South Russell Street has been demolished, making this task even harder for future generations!)

 

Outlines of buildings from the 1874 and 1885 maps over the modern landscape.

Outlines of buildings from the 1874 and 1885 maps over the modern landscape.

Once we georeferenced the maps, we traced the buildings from them so that we could view the modern landscape and the historic building outlines. Looking at the outlines of the buildings from the two maps, it is clear that the relationship between the maps and the modern landscape is not straightforward. Many of the same buildings are represented, but they fall in different places (the two at the north [left] end of the view, for example). Some of the differences between the maps indicate actual changes to the built landscape between 1875 and 1885, such as the remodeling of the buildings on the lot immediately south of the 1827 school and the demolition of the most southern buildings. Other differences, however, raise questions about the accuracy of the different elements of the maps. For example, the 1827 school is depicted on both maps, but when both maps are georeferenced, the school building does not appear in the same location. The Beers map also shows buildings projecting well into the street (which is possible if the street was widened, or it may represent an error in the generation of the map), while the Sanborn map conforms somewhat better to the modern street layout. The Beers map also labels the buildings by owner or occupant, but the individuals listed in the project area (S. Bartlett and J. C. Barnes) were no longer property owners in 1874, and in fact, had both owned the same property in succession, not adjacent properties. It is not uncommon for historic maps not to conform to a modern survey of the same landscape: streets could be changed; buildings could be moved. More than that, however, historic maps are historic documents, like any other, that need to be read critically. Was the map maker concerned with accurately showing the streets, perhaps, but not the property lines or the locations of the buildings? With the limited amount of excavation data that we have, we cannot be certain about the accuracy of either map; both may be somewhat correct and incorrect in different ways. Critical evaluation of the maps indicated that we also needed to do deed research to trace the owners, uses, and sizes of the parcels on this part of Burial Hill.

To be continued…

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