Submitted by dinnerkettle, who says:

Inherited this MBTA keychain from my aunt recently. There’s no exact date on it, but it was definitely made before the red line got extended past Harvard and before some other stops got renamed.

Transit Maps says:

What a great piece of transit map-related ephemera! The best I can date it is after 1980 (when Braintree opened; an arrow points to it at the bottom right of the map), but before 1984 (when the Red Line extended past Harvard to Porter). Also of interest is the extension of the “E” branch of the Green Line all the way to Arborway: this was cut back to Heath Street in 1985.

While obviously based on the classic Cambridge Seven Associates “spider map” that first appeared in 1968, there’s a very curious misspelling of Northampton station as Northhampton (note the extra “h”), which makes me believe that this was produced by a third party vendor under license from the MBTA.

It also looks like the artwork was screen printed in five separate colours: red, green, blue and yellow/orange for the route lines and black for the stations and type. The Blue Line is registered terribly, almost completely missing the station markers along it.

UPDATE: A little more sleuthing and help from David Sindel leads me to revise the date to c. 1978-1979. “Columbia” instead of “JFK/UMass” definitely dates it prior to 1982, and his reasoning about the alternate Harvard stations in the early 1980s is sound.

But the kicker is actually in the map itself, which uses black dots for the stations. By 1980, all stations except the four main interchange stations in the middle of the map were shown using white dots, and the western end of the Red Line had been flipped up at a 45 degree angle.