I'll answer the question after I get a few answers/guesses.
Update 3/3/11: You all seemed to have either 1.)cheated well, 2.) recognized it quickly, or 3.) played dense. Congratulations to all of you. Here are the details:
The installation is in the sidewalk in front of the SoHo Building at 110 Greene Street, between Prince and Spring. It's titled "Subway Map Floating on a New York Sidewalk," and it was created in 1986 by Francoise Schein, a Belgian artist and architect. The schematic runs the length of the building -- 87 feet -- and is 12 feet wide.
The IRT, BMT and IND are represented by half-inch-wide stainless-steel bars embedded in concrete, with lights indicating SoHo-area subway stops. The project cost an estimated $30,000 to produce and won the City Art Commission award for the best art project that year. It only represents the Manhattan part of the system and it's modeled after the 70's version of the subway map which was stylized instead of strictly "geographically correct".