The Appalachian trail is the brainchild of Benton MacKaye who came up with the idea while working on projects related to regional planning for the United States governement. In 1921 he published an article titled "An Appalachian Trail: A Project in Regional Planning" in which he outlined the four chief features of the project: the trail, shelter camps, community groups, and food and farm camps. MacKaye saw the project as a way to "establish a base for a more extensive and systematic development of outdoors community life."
This map is an early sketch of the proposed route from Mt. Washington in New Hampshire to Mt. Mitchell in North Carolina. MacKaye suggested a "'long trail' over the full length of the Appalachian skyline, from the highest peak in the north to the highest peak in the south."
A guide to the MacKaye family papers is available online.