Mr. D’Adamo’s entry, along with two others, won first place. The winning designs were given to the transit authority, and the color-by-route concept was incorporated into an official redesign of the map by 1967. All versions of the subway map since have been based on color coding by route.

Mr. D’Adamo’s original map never became official, partly because the contest rules had demanded a geographically accurate layout of the city, but the transit authority later decided to go with a design where the geography was more loosely depicted, Mr. D’Adamo said.

His original map was lost, he said.

But while cleaning out old boxes in 2014, Mr. D’Adamo found a color photograph of his map. He collaborated with the graphic designer Reka Komoli and the historian Peter B. Lloyd, who is writing a book about the history of New York’s subway system, to digitally restore the map.

In the years between the contest and the map’s rediscovery, Mr. D’Adamo found his calling — in transportation. After winning the contest, he quit his job as a lawyer and joined the M.T.A., where he worked for five years before becoming Westchester County’s first commissioner of transportation.