Prototype State index to topographic maps and other map products.-The present system of providing information on the availability and coverage of cartographic data was critically reviewed. The first result is a new format for State map sales indexes, redesigned to improve readability and economy of maintenance. The new Virginia index map (fig. 36, p. 83) in black, gray, and red is much easier to read than the former light-green rendition with black overprint. One standard fold will replace the 11 fold sizes now used. New typefaces were chosen, and insets were added to show coverage in several map series. Two companion catalogs, one for published maps and the other for map data, with detachable order forms, will accompany the new index map.

• Cartographic applications of satellite imagery.The studies of cartographic applications of satellite imagery continued, with both Landsat-1 and -2 still functioning. A 1:500,000-scale satellite image mosaic of Georgia (fig. 37) that shows the general extent of the flood plains was prepared for State use in regional geologic studies. A fundamental problem is the best way of processing Landsat data for distribution in image form. A second edition of the Upper Chesapeake Bay satellite image map shows the improvement due to digital image processing. Other experiments indicated that conventional photoprocessing of spectral records into a color composite may not

be optimum for some mapping purposes. Consultation and coordination with mapmakers and others throughout the world indicate that cartographic applications of Landsat data are manifold and accelerating. For example, Canadians are using Landsat imagery to revise maps at scales as large as 1:50,000, and the U.S. Defense Mapping Agency has used the imagery to revise hydrographic charts of international waters. However, should operational spacecraft retaining the basic specifications of the experimental Landsats be launched to maintain the established sequence and flow of repetitive and consistent coverage now relied on by several nations that have established receiving stations, it must be understood that the data are directly usable only at small scales-generally 1:500,000 and smaller. Experience shows that Landsat imagery must be supplemented by other more detailed and larger scale data to provide cartographers with all the information they need to produce complete topographic maps at scales of 1:250,000 and larger.

References

Bureau of the Budget, 1967, Coordination of surveying and mapping activities: Bureau of the Budget Circular A-16 (revised), May 6, 1967, 3 p.

U.S. Geological Survey, 1976, Mapping-An annual report of USGS cartographic research: USGS Topographic Division, 520 National Center, Reston, Va. 22092, 75 p.