are scribed on a single scribecoat sheet for overprinting in purple on the published map. About 
9 months are required for interim revision and preparation of the manuscripts for printing. 
Publication 
The interim-revision edition of a map requires an additional press impression in order 
for the contents of the revision plate to be overprinted on the map in purple. The map user can 
instantly recognize the features that have been updated, as well as areal development trends. 
ORTHOPHOTO PRODUCTION 
  
Definitions 
USGS has adopted the term orthophotoquad to represent a photomap of standard accuracy 
prepared in quadrangle format from an orthophotograph (or a mosaic of orthophotographs) with 
minimal cartographic treatment. The orthophotoquad contains projection neatlines with latitude- 
longitude and State grid ticks, the UTM grid superimposed on the photoimagery, labels for a few 
principle features, and a map border. An orthophotoquad is produced in about 1 year, and a pre- 
liminary version--the advance orthophotoquad--can be prepared in about 4 months. The advance 
orthophotoquad contains geodetic reference information and minimal collar information, all provi- 
ded by an automatic plotter (USGS Autoplot). 
  
Aerial photography 
  
Aerial photographs for producing orthophotoquads are usually taken at flight heights suf- 
ficient to cover the area of an entire 7.5-minute quadrangle with a single exposure and so that every 
other exposure is quad-centered. Thus, for superwide-angle cameras a 6,700-m (22,000-ft) flight 
height is used to obtain quad-centered photographs, and for wide-angle cameras a flight height of 
about 12,900 m (40,000 ft) is used). The higher-altitude flying requires a Learjet-type aircraft. 
Field surveys 
Since orthophotoquads do not include contours, field surveys are needed primarily to obtain 
horizontal ground control and name information. Control for aerotriangulation is desired at a mini- 
mum spacing of 15 minutes around the perimeter of the project and at 30-minute spacing within. 
Since many project areas already have closer spaced control, the fieldwork required is often no 
more than identification of existing control and establishment of a few new control points at strate- 
gic locations. 
Cartographic treatment 
  
Orthophotoquads require very little manual drafting. The projection lines ; geographic, 
State plane-coordinate, and UTM ticks ; and necessary lettering are provided automatically by 
the USGS Autoplot. Although the quality of Autoplot drafting is not considered adequate for litho- 
graphic printing, the information can be produced rapidly and clearly enough to justify its imme- 
diate availability as a provisional map--the advance orthophotoquad. The finish orthophotoquad, 
however, must meet the applicable cartographic standards established for all maps produced by 
the USGS. 
Publication 
Since advance orthophotoquads are not intended for wide distribution, they are reproduced 
by the diazo process from a screened film positive as the master plate. Distribution of the diazo 
prints is handled by the USGS Mapping Center responsible for the region in which the project area 
is located. The United States is divided into four regions for mapping, with a region assigned to 
each USGS Mapping Center. A fifth USGS Mapping Center serves all four regions for production of 
small-scale and special maps and for revision of both 1:24 000-scale and small-scale maps as 
workload dictates. 
Orthophotoquads are reproduced in black-and-white by photography, the diazo process, 
lithography, or all of these, depending on the projected distribution or established demand. Limi- 
ted quantities of lithographed orthophotoquads are stocked for sale to the public through regular 
map sales channels. 
REVISION CRITERIA 
  
Priorities for revising maps are based on requests from map users and the degree of 
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