adjective

Define:  capable of being perceived especially by the sense of touch
Source: http://www.merriam-webster.com/dictionary/tangible

Fort Greene Dreams pg34 ; “One Tangible document of the creative ferment in Fort Greene, and the overall New York black community, was a photo taken by Anthony Barboza for an unpublished  The New York Times Magazine piece on the “new black aesthetic” by  Trey Ellis in 1989.

Tangible means that something can be touched. Nelson George was referring to a document that actually exists and can be accessed was a photo taken by Anthony Barboza.