Greenpoint's problem is age plus growth. Flags poured generations ago have been lifted by street trees that were saplings when the concrete went down, and along the waterfront, brand-new buildings meet those old sidewalks at grades that no longer line up. The result is exactly what DOT cites: steps between flags of half an inch or more.
We fix the cause, not just the symptom. Replaced flags get a properly compacted base and a tree pit sized for the tree that is actually there, and where new construction meets old sidewalk we set the new concrete to meet the existing grade with a clean joint instead of a trip hazard.