CHAPTER IX

THE PLAIN FROM THE AIR

(FIGS. 34 TO 41)

A RIVER ON THE GREAT PLAINS

The difficulty of photographing a plain from a point on its surface needs no emphasis, but its successful representation by means of air photographs is illustrated by many figures in this book. The Great Plains of the west-central part of the United States are illustrated here by a view of the Red River (Fig. 36), which shows the flat surface of the land and the broad sandy bed of the river only partly covered by the intricately woven strands of the braided channels--a scene characteristic of the Great Plains.

MEANDERING STREAMS ON THE COASTAL PLAIN

The ox-bow curves of meandering streams are among the features of the earth’s surface most familiar to the student of physical geography; yet, heretofore, they have been illustrated only by maps, constructed at great labor and expense. Comprehensive photographs of them are rare and are, at best, imperfect and unsatisfactory for purposes of illustration. On the other hand, meandering streams lend themselves admirably to air photography. Equally familiar to the student of geography and physiography is the term “abandoned meander.” These ancient stream courses, many of which are now occupied by marsh, brush, or forest, have been still more difficult to illustrate by means of photographs. In some instances wooded meanders like those near Columbus, Ga. (Fig. 34), long ago abandoned by the stream that formed them, are shown in air pictures in a manner but little less conspicuous than the meanders of the present-day stream. It is believed that instructors will find Figure 34 useful, not only in illustrating meandering streams and abandoned meanders but also in showing how meanders develop.

THE GLACIAL DRIFT PLAIN

Some of the characteristics of a third type of plain, the glacial drift plain, are shown in Figures 37 to 41. Here are pictured glacial lakes, bogs, marshes, moraines, and outwash plains, peat-filled depressions, kettleholes and gullied slopes--typical features of a glaciated region. The views show, also, many of the familiar aspects of the central and western parts of the United States: the rectangular pattern formed by the land subdivisions established by the United States Land Office, the checkerboard pattern being emphasized by the section-line roads; the minor subdivisions into fields; and the cultivation of a variety of crops.

These photographs were selected from a series taken as an experiment in map-making. In June, 1920, the United States Air Service sent a plane equipped with a K-1 camera from Dayton, Ohio, to Schoolcraft, Mich, where in seven hours’ flying time a fifteen-minute quadrangle, about 220 square miles, was photographed. The prints were matched together and reduced to a scale of 1:48,000. From them such features as roads, streams, forests, land corners, etc., were transferred to plane-table sheets, which the topographic engineers on the ground then used for contouring the relief. Figure 38 is a part of the preliminary proof of this map. It may be added that the experiment is regarded as highly favorable to the use of the airplane camera as an instrument in mapping.