RED=Square 483, GREEN=Square N-515
The Steuart Investment Properties website has the following to say:
Square 483 (New York Avenue, 6th, 5th and K Street, NW)
The Property is located across 5th Street from Safeway and City Vista, one block east of the Washington, D.C. Convention Center and four blocks north of the Verizon Center. This entire city block, totaling 56,350 square feet, is zoned DD-C3C under the Mount Vernon Triangle Overlay. The development planned totals 535,000 square feet of office and commercial space on twelve floors with below grade parking.
Square N-515 (New York Avenue, 4th and L Street, NW)
The site encompasses 76,000 square feet of land supporting a two-building, mixed-use development and is zoned DD-C3C under the Mount Vernon Triangle Overlay. The property is located across L Street from Safeway and City Vista, two blocks east of the Washington D.C. Convention Center and five blocks north of the Verizon Center.
The Mount Vernon Triangle CID map labels Square 483 as a 550,000sf office building with ground level retail and a street address of 501 K St NW. That's the extent of what I know. Google and Washington Business Journal have come up empty for me. So I turn to our readers with great anticipation to unleash their knowledge.