2008-2009 Great Lakes Border Ortho Imagery

An orthoimage is remotely sensed image data in which displacement of features in the image caused by terrain relief and sensor orientation have been mathematically removed. Orthoimagery combines the image characteristics of a photograph with the geometric qualities of a map. For this dataset, the natural color orthoimages were produced at 0.3-meter pixel resolution (approximately 1-foot). The design accuracy is estimated not to exceed 6 meter horizontal RMSE for locations within the United States. Each orthoimage provides imagery for a 1500-meter by 1500-meter block on the ground. The projected coordinate system is UTM with a NAD83 datum, spheroid GRS80. There is no image overlap between adjacent files. The naming convention is based on the U.S. National Grid (USNG), taking the coordinates of the SW corner of the orthoimage.

These data have been created as a result of the need for having geospatial data immediately available and easily accessible in order to provide geographic reference for federal, state, and local emergency responders, as well as for homeland security efforts. Orthoimages also serve a variety of purposes, from interim maps to field references for earth science investigations and analysis. The digital orthoimage is useful as a layer of a geographic information system. These data can be used to provide reference information for web browsers and for map applications at a scale of 1:100,000 or smaller.

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Natural color orthoimagery is organized in three color bands or channels which represent the red, green, and blue (RGB) portions of the spectrum. Each image pixel is assigned a triplet of numeric values, one for each color band. Numeric values range from 0 to 255. Pixels outside the project boundary are represented with the numeric value of 0,0,0.

U.S. Department of the Interior, U.S. Geological Survey, 1996, Standards for Digital Orthophotos: Reston, VA.

Users must assume responsibility to determine the usability of these data.

Any downloading and use of these data signifies a users agreement to comprehension and compliance of the U.S. Government Standard Disclaimer. Insure all portions of metadata are read and clearly understood before using these data in order to protect both user and U.S. Government interests.

There is no guarantee of warranty concerning the accuracy of the data. Users should be aware that temporal changes may have occurred since this data set was collected and that some parts of this data may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its limitations. Acknowledgment of the originating agencies would be appreciated in products derived from these data. Any user who modifies the data is obligated to describe the types of modifications they perform. User specifically agrees not to misrepresent the data, nor to imply that changes made were approved or endorsed by the U.S. Government.

ArcGIS 9.3.1; MicroStation v7; Z/I Imaging ISAT 5.3 and Orthopro 5.3

Sample points taken from overlapping areas of adjacent image frames along a single flight line and between strips along adjacent flight lines are typically consistent to the 2-3 pixel level. This not only ensures that a consistent mosaic can be created from the adjacent frames and image strips acquired with the DMC digital frame mapping system but also means that the images have good precision and as a group are spatially self-consistent.

The accuracy value for locations within the United States was determined by measuring photo-identifiable control points collected with GPS survey methods in the orthophotos.; Quantitative Value: 6.0 meters, Test that produced the value: FGDC Geospatial Positioning Accuracy Standards, Part 3: National Standard for Spatial Data Accuracy (NSSDA)

Pixels outside the project boundary are represented with the numeric value of 0,0,0.

Compliance with the accuracy standard was ensured by the use of photo identifiable ground control points and/or the collection of airborne GPS data.