Map 7 (Mandatory Sidewalk Widenings and Publicly Accessible Open Area), in Appendix A of this Chapter, shows locations of mandatory sidewalk widenings in the East River Subdistrict. The depth of such sidewalk widenings shall be as indicated on Map 7 and shall be measured perpendicular to the street line unless otherwise indicated. All sidewalk widenings shall be improved to Department of Transportation standards for sidewalks, shall be at the same level as the adjoining public sidewalk, and shall be accessible to the public at all times.