The Eastern Rail Yards were rezoned as part of the 360-acre Hudson Yards Rezoning , approved by the City Council in January 2005. This massive rezoning, creating the Special Hudson Yards District, was intended to increase the commercial and residential capacity of the Far West Side between West 28th and West 43rd Streets, and Eighth and Eleventh Avenues. According to the Department of City Planning, purposes included:
- To expand the Midtown business district to increase office space and make Manhattan more "economically competitive"
- To anticipate the expansion of the 7 train West to 11th Avenue, and downtown to 34th Street
- To encourage expansion of the Javits Center by the creation of a "Convention Center Corridor"
- To make a new open-space network, including the creation of a new midblock pedestrian avenue running from 33rd to 41st Streets
- To interact with a planned Jets football stadium on the Western Rail Yards (not part of this rezoning) related to the NYC2012 Olympic bid
More information on the Hudson Yards rezoning can be found here  (DCP) and here  (CB4).
So how does the rezoning affect the Rail Yards development?
The MTA's Request for Proposals for the Eastern Rail Yards (available here  as a PDF) upholds the land use criteria laid out as part of the rezoned Special Hudson Yards District. This means the buildings and open space at the Eastern Yards will relate north and east, in the context of the larger Hudson Yards area (all the way up to 42nd Street). However, from an urban design perspective, the Eastern Yards site is not necessarily related to the Western Rail Yards, which was not part of the rezoning.
ULURP  process, as well as City and State Environmental Review. The MTA has stated that Eastern Rail Yards development will begin as soon as possible, independent of the timeline of this review.