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GIS Education & Resources

Digital Orthophotos of Southeastern Wisconsin

 

A digital orthophoto (DOP) is an aerial photograph taken of the earth that has been electronically scanned and corrected for distortion to create a digital raster image of the ground that is accurate enough for mapping and measuring purposes. In the spring of 1995, the seven-county area of southeastern Wisconsin was flown for DOPs at a height that captured ground images at a scale of 1" = 1667', and a ground resolution of two feet. The Southeastern Wisconsin Regional Planning Commission (SEWRPC) produced the digital files and have made them available on CD-ROMS. Files from four of the seven counties are available for students, faculty, and staff on campus through the Golda Meir Library's AGS Collection.

 

Each DOP file covers an area of roughly four square miles (four adjacent sections) and is approximately 30 megabytes in size, stored in TIFF (TaggedImage File Format) raster format. The entire series of files provides a unified digital image base of the following southeastern Wisconsin counties: Milwaukee, Ozaukee, Washington, and Waukesha, and includes images of buildings, streets, sidewalks, trees, and other visible features that are generally larger than two feet on the ground.

 

Since the DOPs were produced to meet National Map Accuracy Standards (at a scale of 1" = 400'), and since they contain Wisconsin State Plane Coordinates (based upon the North American Datum of 1927), they can be easily combined with the digital quarter section maps of the city of Milwaukee that are available on the University's computer network. This allows the display of legal parcel boundaries and public right-of-way directly onto the photograph, and, hence, linkage to property attribute data in the Milwaukee Property File (MPROP) via parcel number (Tax Key Number.

 

When used with geographic information systems (GIS) software, the land and buildings shown on the DOP images can be related to their parcel maps from the digital quarter section maps and their attribute data from MPROPwhich describe each building and its parcel (owner, assessed value, year built, land use, zoning, etc.) Alternatively, GIS software can be used to locate and display the aerial photograph of a building or group of buildings when provided with an address or some other characteristic such as owner name, land use, assessed value, etc.

For additional information about accessing the DOPs, contact agsl@uwm.edu at the AGS Collection of the Library.