`"Crosswalk" shall mean that part of a roadway, whether marked or unmarked, which is included within the extension of the sidewalk lines between opposite sides of the roadway at an intersection`

Per https://www.nyc.gov/html/dot/downloads/pdf/hwyrules.pdf , that's what NYC DOT thinks. Crosswalks don't require markings or curb-cut ramps. They don't even *follow* the markings or ramp cutouts -- they follow the line of the sidewalk.