The Use of Aerial Photos in Engineering Planning

The planning of any engineering project requires information on land use, topography, soils, drainage, transportation, urban de­ velopment, and many other factors before actual location and design can be accomplished or field surveys undertaken. To obtain this preliminary information engineers surveyors, and planning com­ missions need maps. They need planimetric maps showing land use, or they need topographic maps having a contour interval of at least ten feet showing planimetric detail. Unfortunately, in numerous counties of Indiana and in the various cities of the state planimetric and topographic maps are seldom available or are obsolete. For example, of the 600 odd minute quadrangle sheets that are required for mapping the state of Indiana only about 130 maps were completed before January 1951 (10). Although 35 have been issued since that date, this great undertaking is still less than 30 per cent complete. Furthermore, the cost and time required to prepare by field survey methods the different types of maps would deplete available funds and in all probability prevent the construc­ tion of the improvement or delay it for a long period of time. In addition to the shortage of maps there is a shortage of engi­ neers for collecting and compiling information into maps. This shortage is especially felt by the county, city and state governments at a time when population is increasing; and, therefore, needs for water supply, sewage treatment, parking facilities, subdivision develop­ ment, highway development, traffic studies and other engineering studies are critical. Aerial photographs are a valuable source of basic map information to overcome the shortage of maps and also save time and money in numerous planning operations. It is the purpose of this paper to discuss the characteristics of aerial photographs and to explain their use in the planning phases of engineering projects. It is to be emphasized that aerial photographs will not eliminate