In 1921, the Airways Section of the United States Army Air Service (later Army Air Corps) established a Model Airway to develop and test new methods of conducting scheduled cross-country flights over varied terrain and for investigating various aids to navigation, including aeronautical charts. The Air Service’s Model Airway initially extended some 400 miles from Washington to McCook Field, Ohio, but was expanded in 1923 to include airfields in New York and a number of mid-western states. Eventually it covered most of the major cities in the East and Midwest.
Shortly after the establishment of the Model Airway, the Air Service initiated an exhaustive evaluation concerning the question of aeronautical charts in an effort to develop a “Standard Map for Aerial Navigation.” More than 300 pilots were interviewed during flights along the airway or responded to questionnaires. In addition, existing commercial and military air navigation maps produced in the United States, Italy, and France were examined. Deputy Director of the Air Service General William (Billy) Mitchell then authorized the production of a series of air navigation maps based on the standards developed from these studies with instructions that they be prepared under contract by either the Rand McNally or Clason map companies of Chicago, but the U. S. Geological Survey, persuaded the Air Service that the Survey could produce these maps quicker.
Two of the first experimental maps, compiled jointly by the Geological Survey and U. S. Army Engineer Reproduction Plant (later U. S. Army Map Service) pertained to the route between Dayton, Ohio, and Washington, D. C. They were issued in the form of strip maps for use in mechanical roller devices. Each strip map covered an area about 80 miles by 220 miles at a scale of 1:500,000, the same scale still used today for standard visual sectional charts issued by the Federal Aviation Administration. Only major towns, roads, and railroads were depicted for quick reference from the air. Terrain was shown by spot heights, gradient tints, and contours at 500 feet intervals (an idea borrowed from the 1:1,000,000 scale International Map of the World). The color yellow indicated urban areas while red denoted all aerial navigation information such as landing fields, flying routes, and compass bearings, conventions that became standard worldwide. Flight distance was indicated in miles along flight routes, at ten-mile intervals. A red arrow indicated compass variation.
The Army Air Service and Air Corps eventually issued 63 air navigation maps between 1923 and 1933, covering the major military air routes in the United States. With the passage of the Air Commerce Act of 1926 responsibility for preparing air navigation strip maps shifted from the Army to the newly established Commerce Department and its mapping arm, the U. S. Coast and Geodetic Survey. This new mapping program was designed to link an emerging commercial airways system with the existing military network. Between 1927 and 1936, the Coast and Geodetic Survey’s Airways Mapping Section published 43 strip maps. They were similar in design, content, format and scale to the Army Air Corps’ strip maps, on which they were modeled.