Post route map of Maryland, Delaware, and D.C.

This post road map of Maryland, Delaware, and the District of Columbia shows the postal routes designated for those areas as well as part of New Jersey. The map was published by the Post Office Department in July 1917. The month of July marked the beginning of the Department's new fiscal year and was also the month that new postal route maps were released.

Although not designed for airmail service, this map was used in that way. Early airmail pilots had few instruments, and most relied on markers on the ground for navigating. This map shows the folds that a pilot made in the map so that he could attach it to his leg and easily check it while sitting in the cockpit. The pilot navigated by comparing the map attached to his leg with the landscape and markers (such as railroad tracks) on the ground.

The map was approved for this use by Capt. Benjamin B. Lipsner, who assisted with the organization and operation of the first airmail flights in 1918. Lipsner marked his approval on the map with the date May 11, 1918, four days prior to the first airmail flights.