OVERVIEW

The U.S. Geological Survey created these orthophotos as part of its National Aerial Photography Program (NAPP). They were post-processed by MassGIS to conform to same tiling scheme and projection as the MassGIS 1:5000 black and white orthophotos. The original products are 1-meter ground resolution, quarter-quadrangle (3.75-minutes of latitude by 3.75-minutes of longitude) images cast on the Universal Transverse Mercator Projection (UTM) on the North American Datum of 1983 (NAD83). The geographic extent of the DOQ is equivalent to a quarter-quad plus an overedge ranging from 50 meters to 300 meters beyond the extremes of the primary (NAD83) and secondary (NAD27) corner points. The overedge was included to facilitate tonal matching for mosaicking and for the placement of the NAD83 and secondary datum corner tics.

USGS created raster images by scanning 1:40,000 scale aerial black and white photograph film diapositives with a precision image scanner, using an aperture of approximately 25 to 32 microns. The scanner converted the photographic image densities to gray scale values ranging from 0 to 255. Scan files with ground resolution less than 1 meter or greater than 1 meter but less than 1.28 meters were resampled to 1 meter. All DOQs are cloud free within the 3.75' image area. Source photography was leaf-off in deciduous vegetation regions. 

Ground control points in UTM NAD83 were acquired from ground surveys or developed in aerial triangulation models and are third order class 1 or better, and meet National Map Accuracy Standards (NMAS) for 1:12,000-scale. Horizontal and vertical residuals of aerotriangulated tie-points are equal to or less than 2.5 meters. Rectification was accomplished using Digital Elevation Models (DEMs) covering the same area as the scanned image, ground control points, orientation parameters, and a camera calibration report. All data was inspected according to a quality control plan and tested for attribute accuracy, logical consistency, data completeness and horizontal positional accuracy. 

MassGIS took the USGS images and mosaicked and projected them to the Massachusetts State Plane Coordinate System, NAD83 Mainland Zone using the ARC/INFO GRID module. The projected grids were clipped to the MassGIS Orthophoto Index and converted to grayscale images. The 1-meter images (15 megabytes each) were resampled for 2- (4 mb) and 5- (640 kb) meter resolution. All three resolution images are stored in tiff format with .TFW header files. The images are named according to their resolution and Orthophoto Index SHEET-ID, separated with the letter ‘u’ to distinguish them from overlapping 1:5000 orthophotos (example names: 1u125918.tif, 2u125918, 5u125918.tif).

There are no attrribute for the images. Each pixel is coded with a gray-shade value ranging from 0-255. Full metadata on the original USGS product is available from the USGS web site at http://online.wr.usgs.gov/ngpo/doq/.

These images are available for Franklin County and parts of southeastern Mass. Original dates of photography, obtained from the USGS images’ headers, are April 28, 1992, and April 1995. For details of the areas covered please see the Status Map.

The datalayer is maintained by MassGIS. Also see MassGIS' ortho image layers: Color | Black and White.

Please note that MassGIS does not have any old aerial photographs (pre-1992). For information on such products please see http://erg.usgs.gov/isb/pubs/factsheets/fs12796.html.

Last Updated 9/28/2005
EOEA Disclaimer | Privacy Policy