U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 039-00

March 2000

A digital orthophoto quadrangle (DOQ)

is a computer-generated image of an

aerial photograph in which image

displacement caused by terrain relief 

and camera tilts has been removed. It

combines the image characteristics of a

photograph with the geometric qualities

of a map.

Characteristics of a USGS Digital

Orthophoto Quadrangle

The standard DOQ’s produced by the

U.S. Geological Survey (USGS) are

either gray-scale or color-infrared (CIR)

images with a 1-meter ground resolution;

they cover an area measuring 3.75-

minutes longitude by 3.75-minutes

latitude, or approximately 5 miles on

each side. Each DOQ has between 50

and 300 meters of overedge image

beyond the latitude and longitude corner

crosses embedded in the image. This

overedge facilitates tonal matching and

mosaicking adjacent images. 

The standard DOQ is formatted with an

ASCII keyword header followed by a

series of 8-bit binary image lines. CIR

DOQ’s are 24-bit band-interleaved-bypixel (BIP) images. The header contains

a wide range of data for identifying,

displaying, and georeferencing the

image.

All DOQ’s are referenced to the North

American Datum of 1983 (NAD 83) and

cast on the Universal Transverse

Mercator (UTM) projection. Primary

(NAD 83) and secondary (NAD 27)

datum coordinates for the upper left pixel

are included in the header so that users

can spatially reference other digital data

to the DOQ. 

The file size of a gray-scale DOQ is 40-

45 megabytes, and a color-infrared DOQ

can be three times this size.

Producing a Digital Orthophoto

Quadrangle

To produce a DOQ requires (1) a

minimum of three ground positions that

can be identified on the photograph to be

rectified, (2) camera calibration

parameters, such as the calibrated focal

length and the coordinates of the camera

fiducials, (3) a digital elevation model

(DEM), and (4) a digital image produced

by scanning an aerial photograph with a

precise, high-resolution scanner. 

The digital image is rectified to generate

an orthophoto by processing requirements 1 through 3 above for each image

picture element (pixel), using rigorous 

photogrammetric equations on a compuDigital Orthophoto Quadrangles

Image from part of a digital orthophoto quadrangle of Washington, D.C.
ter. The finished product is a spatially

accurate image with planimetric features

represented in their true geographic

positions.

Accuracy Requirements

The accuracy and quality of USGS

DOQ’s must meet National Map

Accuracy Standards at 1:12,000 scale for

3.75-minute quarter quadrangles and at

1:24,000 scale for 7.5-minute

quadrangles. Accuracy and quality

depend on the following: 

• photographs that meet National Aerial

Photography Program standards, which

are quarter-quadrangle centered. The

photographs are exposed at a flying

height of 20,000 feet above mean terrain; 

• a DEM with the same area coverage as

the DOQ and that is equal to or better

than a level 1 USGS DEM having a rootmean-square error in elevation no greater

than 7 meters; 

• a highly accurate image-scanning

process that uses a scanning aperture

between 7.5 and 32 micrometers (μm). A

1:40,000-scale image scanned with a 25-

μm aperture produces a ground sample

distance of approximately 1 meter; and 

• identifiable ground control positions

with coordinates acquired from ground

surveys or aerotriangulation. 

Uses for Digital Orthophoto

Quadrangles

A DOQ can be incorporated into any

geographic information system (GIS)

that can manipulate raster images. It can

function as a cartographic base for

displaying, generating, and modifying

associated digital planimetric data. Other

applications include vegetation and

timber management, routing and habitat

analysis, environmental impact assessments, emergency evacuation planning,

flood analysis, soil erosion assessment,

facility management, and ground-water

and watershed analysis. The accuracy

and extraordinary detail provided by the

DOQ allow users to evaluate their data

for accuracy and completeness, make

real-time modifications to their data, and

even generate new files. 

Distribution Media

DOQ’s are distributed in either native

(standard) or GeoTIFF format on a

variety of media, including 8-mm tape,

CD-R, and FTP as uncompressed files.

DOQ’s covering selected counties are

also available packaged as individual,

JPEG-compressed files. Note that the

county DOQ products contain DOQ’s

built to the pre-1997 (old) standard and

do not contain the keyword header.

Obtaining Digital Orthophoto

Quadrangles

DOQ files are available from the USGS

Sales Data Base and can be ordered

online through the Global Land

Information System (GLIS) at 

edcwww.cr.usgs.gov/webglis or by

contacting any Earth Science Information

Center (ESIC). DOQ coverage is not

available for all areas in the United

States.

Additional Information

More information about DOQ’s can be

found at edc.usgs.gov/Webglis/glisbin/

guide.pl/glis/hyper/guide/usgs_doq.

For information on other USGS products

and services, call 1-888-ASK-USGS, use

the ASK.USGS fax service, which is

available 24 hours a day at 703-648-4888,

or visit the general interest publications

Web site on mapping, geography, and

related topics at mapping.usgs.gov/

mac/isb/pubs/pubslists/index.html.

Please visit the USGS home page at

www.usgs.gov.