GIS Tools for the City Archaeologists

The City archaeologists use Geographic Information Systems (GIS) to improve the efficiency and accuracy of the archaeological review process.

Page updated on Sep 3, 2020 at 2:53 PM

GIS Tools for the City Archaeologists

The Alexandria Archaeological Protection Code, the first of its kind in America, became a part of the City’s Zoning Ordinance in 1989. Archaeologists review all development projects in the City to ensure that information and resources from significant sites are recovered prior to construction activity, and to encourage protection of sites in situ. The use of GIS improves the efficiency and accuracy of the review process, thus enhancing Alexandria’s historic preservation efforts. Historical maps and aerial photographs are scaled to serve as layers within the City’s Geographical Information System in order to predict topographical locations of Native American occupation and to identify the locations of historic sites on the contemporary maps. Alexandria Archaeology worked with the Center for Geospatial Information Technology at Virginia Tech, and with the City of Alexandria’s GIS Division in the Department of Planning and Zoning, to develop historical map layers.

As a result of the archaeological review process, many sites have been investigated, and a wide variety of important information has been made available to the public. The kinds of sites and resources explored and preserved as a result of the Code include Native American camps, tenant farmsteads, Civil War encampments, plantations, cemeteries, African American homes, and businesses, including a sugar factory, a ropewalk, grist mills, potteries and glassworks.

Protection of Historic Resources 

To protect archaeological sites from potential looting, some of the map layers will only be used in-house, and will not be made available to the public. The exact location of archaeological sites is protected and is not subject to the Freedom of Information Act. Federal and State governments restrict this information, and ask that we do the same. We may make location information available when the site is no longer extant because of archaeological excavation and subsequent development.

Overlay Maps AR GIS Overlay small image

GIS overlays allow City archaeologists to identify locations of important historic sites in the modern landscape, and to make decisions about where archaeological investigations need to be conducted prior to development.

This GIS map shows a Civil War map, Environs of Washington, from the National Archives, as an overlay on the modern City map which shows streets and property boundaries. We can also add layers on the modern map showing existing buildings, sewer lines and other features. The map, which covers the entire City, was digitized and “rectified”, or made to fit as closely as possible to the modern City map, by matching known points on the old and new maps.

Source Maps for the Digital Atlas

The Digital Atlas includes historical maps and aerial photographs, as well as resource maps developed by Alexandria Archaeology staff and volunteers. Before the Atlas was developed, Archaeologists consulted paper copies of these maps each time they needed to evaluate a property slated for development. All development requiring Site Plans and Special Use Permits are reviewed in accordance with the  Alexandria Archaeology Protection Code. Archaeologists also review all building permits.

As each map is added to the Atlas, the evaluation process becomes easier. The maps are seen as layers on top of the modern City map, and various layers can be turned on and off. We can zoom in to a property and look at features on the early maps in relation to existing buildings.

Here are a few examples of maps included in the Digital atlas. Some layers are complete, and others are still being added to the Atlas.

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Preservation Maps

These maps are from the City’s Master Plan. In 1992, Alexandria Archaeology created a series of 14 Small Area Plans with maps showing known or possible locations of historic and archaeological resources in each area of the City. These were compiled from a variety of historical and archaeological sources.

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Thematic Maps

These are used for preservation in Old Town. The 35 Thematic Maps were created from a variety of historic sources, each indicating known or possible sites related to prehistory, African American businesses, cemeteries, Quakers, the Civil War, the Fire of 1827, and other topics. These maps, with an underlying database, are gradually being added to the Digital Atlas.

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Historic Maps 

The Civil War Environs of Washington (shown here) was the first historic map layer created for the Atlas. Layers have also been created from the Civil War Quartermaster Maps, and from portions of Alexandria maps from 1748, 1749, 1790 and 1849.

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Aerial Photographs 

Changes in the City over time can be seen in a series of aerial photographs from 1927, 1937 (shown here) and the 1950s. The 1927 map (shown here) was the first to be included in the Atlas. The GIS Division has also posted aerial photos from 1995 to 2006, taken approximately every two years.

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Insurance Maps

The Hopkins and Sanborn Companies created detailed fire insurance maps of American Cities. The Hopkins Insurance map from 1877 (shown here) is our earliest insurance map. The waterfront portion is currently included in the Atlas.