History and Background of the Maps

According to Jefferson M. Moak ("The G. M. Hopkins Company," Mapline, No. 10, June 1978), Griffith M. Hopkins and his brother Henry W. Hopkins founded their own publishing house in Philadelphia in 1865. In the early years, they were involved in county atlas production, but gradually they focused on city plans and atlases. Overall, they produced more than 175 atlases of counties and cities in New England, New York, New Jersey, and Pennsylvania. The company's fortunes declined during the Depression, and it was purchased by the Franklin Survey Company of Philadelphia in 1943.

Hopkins atlases and plat books feature large-scale plates showing lot and block numbers, dimensions, street widths, and names of property owners. These real estate or land ownership maps (also known as plat maps) not only depict property owners, they also show churches, cemeteries, mills, schools, roads, railroads, lakes, ponds, rivers, and streams.

Selection Criteria

The selection objective for the Historic Pittsburgh collection is to cover as many decades and as much geographic area as possible. The selected maps represent an effort to reflect the changing urban landscape of the greater Pittsburgh area from the early 1870s to the late 1930s. Beyond this consideration, priority is given to damaged or deteriorating atlases or plat books that can benefit most from preservation treatment.

Hopkins Real Estate Atlases that were maintained by city departments and bureaus were often systematically updated to reflect extensive housing development, annexation, and street changes within Pittsburgh and the vicinity. Revisions and additions were often ordered from the G. M. Hopkins Co. and pasted onto the original map plates. Newly annexed areas were also noted and stamped by hand in some of the original volumes.

Hopkins Real Estate Atlases have actively been used through the decades, and in many cases, it is rare to find some of these volumes in their original form. The Digital Research Library has acquired some of these revised volumes for inclusion in the Historic Pittsburgh Maps Collection. When researching family history or history of a house, the researcher should pay special attention to revision dates. The Digital Research Library cannot guarantee that the property owners, street names, or city limits presented on some of the online maps were part of the originally published volumes. We have made every effort to note revision dates on the index pages of any volume that has been altered since its publication.

Preservation

To scan the maps, it is necessary to disbind the atlas or plat book (frequently, the original binding is in poor condition). After the books are disbound, the condition of each plate is assessed. Treatment procedures include surface cleaning, mending, deacidification, and encapsulation. After scanning, the plates are either rebound using a post-binding structure or stored in an acid-free flat storage box.

Technical Description of the Maps Collection

The maps in this project are scanned as 24 bit RGB 300 dpi uncompressed TIFF images on a scanner designed for large format engineering drawings. This process is performed by the Chapman Corporation in Washington, Pa.

After the maps and the digitized images are returned to the Digital Research Library, they are compressed using a technology called MrSID (Multi-Resolution Seamless Image Database) from LizardTech. This wavelet compression software allows for the storage and retrieval of large digital images. In contrast to other compression software that relies on tiling, MrSID gets all its sharp resolution from within a single compressed image, and it does not require any special hardware. For example, an original 150 MB uncompressed .tif image file is compressed into 5 MB .sid file.

When a Web user views the maps, a CGI script handles extraction of the appropriate part of the map image from the MrSID file. A unique feature of MrSID is its ability to decompress only that portion of the image requested by the user. Conversion of the extracted component to a .gif image is done on-the-fly and presented to the end user.

For additional information about the Maps project, see "Where Things Were: Historic Pittsburgh Maps", which appeared in the November 2001 issue of the ULS Digital Library News.

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Historic Pittsburgh is hosted by the University of Pittsburgh's Digital Research Library.