Arkansas-White-Red Basins Inter-Agency Committee Purpose, Organization and Plan for Public Hearings

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4110 ob from aerial photographs with frequent ties to horizontal control to obtain more accurate positioning; then frequent cross sections have been made of the river channel itself, so that the river gradient is known. Where the black stream lines have been ticked, the cross sectioning includes that of the river channel and of the river valleys or flood plains adjacent to these streams. The areas shown in Red indicate the extent of topographic mapping of, recent date, which has been accomplished by modern methods of mapping using aerial photographs and stereo compilation for at least the planimetrio bases. This color therefore is indicative of Class 1 mapping, and does not require any revision, as it complies with the National Standard of Map Accuracy requirements, and the contour interval is considered as adequate for any development in the areas. The red which appears irregular on the chart is generally over flood - plain areas, reservoir sites, or on irrigation projects which are usually mapped on a larger scale, than are the general topographic maps. The areas shown in Green indicate the extent of topographic mapping which is considered as adequately mapped. These areas are not as up to date as the Class l category of mapping having been mapped some years ago, prior to the universal use of aerial photographs and stereo compilations Some revision may be required to bring this category of mapping up to Class l standard, so that areas indicated with this green color should be investigated and corrected if necessary, before any development is based on its content. The areas shown in Brown indicate map coverage by planimetry only, and while they are still accurate as guide maps, they would be of little value in any development program. The areas in Yellow indicate the current work, now in progress or planned for early mapping activity. These areas will be or are being mapped to meet the National Standards of Map ,Accuracy. The contour interval chosen will be that which best represents the terrain over an area. PHOTOGRAPHY STATUS This map of the basin area indicates the extent of photographic coverage. You will note that the basin area is well covered by photo- graphs. An analysis of these photographs presents a problem which is difficult to solve, as any analysis depends on the specific purposes for which these photographs are intended. In the map making field, photographs are now used extensively to augment mapping activities. Photographs therefore must be taken under rigid specifications as to flight altitude, focal length of camera, overlap, tilts, flatness of film, etc. The dates on which the present photo coverage was accomplished has an important bearing on their usa- bility for map making, as they aid in the determination of the type of lens used and the overall accuracy of the photographs. C -3