Digital Spatial Data

Aerial Photographs/Orthophotos

Overview

Orthophotos, or orthophotography, refers to aerial photographs that are referenced to precise x, y coordinates on the ground. Referencing removes from the photographs the distortions caused by the terrain, Earth's curvature, and camera angle. Since orthophtos create images that have the characteristics of objects on the ground, one can measure distances, areas, and angles accurately, which makes orthophotos useful for urban planning and other applications. 

Other characteristics of orthophotos are:

• Feature cognition: one can identify and interpret features within an orthophoto by good understanding of feature characteristics (such as size, shape, shadow, pattern, tone, color, and texture).
• Permanent: Orthophotos record objects on the ground in a stop motion and offer a permanent record of a situation or event in relationship to a given point in time. 
• Historical: Many orthophotos have been taken over time by several agencies. Thus, historical orthophotos can offer opportunities to observe or interpret the same geographical coverage overtime.
• Vantage view point: Height adds a viewing advantage not obtainable from the ground = you can see what you cannot normally see!

Most orthophotos are produced by the USDA (Department of Agriculture), but there are also many other photo producers/providers, such as, Federal, state and local government, as well as private sources.

The AGSL collects and archives both paper and digital aerial photos which were taken over time. However, like many other libraries, the AGLS's aerial photo collection is limited to local areas, mostly Milwaukee County. The AGSL also provides digital scanning services which allow patrons to create digital data by their own. For more information on our scanning service, please refer to the Use of Equipment section on the AGSL Services page.

The AGSL has created lists of available aerial/orthophotos for

• Milwaukee County
• Ozaukee County
• Waukesha County
• southeastern WI
• Other areas

The aerial/orthophotos of "other areas" are also available at the AGSL and/or websites (such as USGS or TerraServer.com http://www.terraserver.com/). For assistance in finding and obtaining aerial/orthophotos, please send email to gisdata@uwm.edu. Or please check our Wisconsin data page to check digital orthophoto availability of the Wisconsin counties.

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