CONCLUSION 
Not. so long ago, providing the map user with up-to-date information seemed to be a futile 
effort. The complete revision of a map required years, and by the time the revised version was 
published, it too was out-of-date. Today interim revision is accomplished, ready for publication, 
in about 9 months--compared to about 2 years for standard revision and longer for complete re- 
vision--and the revised maps clearly show all changes in one distinctive color. 
For a more complete revision of the 7.5-minute quadrangle, the orthophotoquad is the 
most expedient means of providing the user with current information. Even though the map user 
must interpret photoimagery, the steadily growing demand for large-area coverage with ortho- 
photoquads is evidence that the orthophoto is a very useful map base. 
Abstract 
Providing the map user with up-to-date information, even for areas already mapped, is one of the most formi- 
dable tasks facing the U. S. Geological Survey. Two approaches are being used in solving the map revision problem. One 
approach is to update a map be preparing an additional press plate containing all revised planimetric features and over- 
printing the revisions in purple on the original map. The other approach is to prepare a companion photoimage map-- 
the orthophotoquad--from current aerial photographs. 
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