REVISION DES CARTES 
ire, UPDATED INFORMATION FOR THE MAP USER 
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U.S. Geological Survey 
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INTRODUCTION | 
It became apparent early in the 1960's that the most important and most difficult mapping I! 
task confronting the U. S. Geological Survey (USGS), the national civilian mapping agency, was | 
It keeping the map user provided with up-to-date bases for those high-priority areas already mapped. 
Many maps become outdated before they are published, especially in areas of urban and suburban 
In development. 
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Providing the user with current map data is now being done expediently in some cases by 
revising only the portion of each map that is grossly outdated and in other cases by preparing an 
additional map, a special type of photo-image map. The first approach is interim revision, and the 
second approach is the preparation of orthophotoquads. Both approaches involve minimal drafting 
: the or other cartographic work. I 
INTERIM REVISION 
  
Definitions ih 
As the revision effort broadened in order to keep pace with maps becoming obsolete, a | 
new terminology developed. Complete revision is the correction of all deficiencies in planimetry 
and relief features to result ın a map that meets current specifications in all respects. Very little 
ives if any, of the original material is salvaged. New aerial photographs are acquired ; field surveys 
are conducted to obtain the necessary control data ; the maps are completely recompiled ; and 
manuscripts are field checked. Over 3 years are required for the complete revision of a 7.5- | 
minute quadrangle, and the cost is about the same as for the original compilation. 
Standard revision is the updating and correction of a map to reflect changes that have 
occured since the original survey or latest revision. In this case much of the original map mate- 
rialis salvaged. The accuracy of the existing map is preserved, and current specifications per- 
taining to map symbolization, content, ánd format are generally applied. New aerial photographs 
are acquired for the revision compilation, and the compilation is field checked. The standard 
revision of a map requires about 2 years. 
Limited revision is the correction of specified map deficiencies only. These deficiencies 
usually involve the updating of certain major features or certain types of features within portions | 
of a total project area. Interim revision is a type of limited revision in which certain planimetric 
features are updated by reference to current aerial photographs. The revised data are not field 
checked and are overprinted in a distinctive purple on the original map. Consequently, this is the 
most expedient of the revision schemes. 
Aerial photography 
The type and scale of aerial photographs used for interim revision depend on the extent 
of the revision, the amount of planimetric detail involved, and the amount of terrain relief. À 
305-mm focal-length camera is often used, enabling revision by monoscopic transfer techniques e 
in areas of moderate relief and in woodland areas. For areas of flat terrain having limited wood- ; 
land coverage, 88-mm focal-length photographs are used. In most cases, however, 153-mm pho- 
tographs are preferred, and they are usually taken at a flight height of 3, 700 m. 
Cartographic treatment ' 
Only selected map features needing updating are treated. Contours are not updated unless 
they are in serious disagreement with the other revised map features. Planimetric detail is deleted 
by scraping the emulsion from the film positive of the planimetric base of the original manuscript. 
The corrected base is then photographed to produce a film negative. This addition--all new data-- 
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