Number of corners: 361
Total signs of change: 278
Corners with no change: 178 (49%)
Corners with changes: 183 (51%)
Newly vacant lots: 4
Major construction or demolition: 16
New buildings: 23
Face lifts: 22
Scaffolding up: 38
Scaffolding down: 15
New signage and/or awnings: 76
New tenants: 63
Newly vacant storefronts: 13
This amounts to 0.77 changes per corner overall; 1.52 changes per corner with change(s). This principally due, I think, to the high correlation between new tenancies and new signage and awnings.
centered in moving five block window
The chart shows the average number of changes per corner, from 16th Street to 108th Street, centered within a 21 corner moving window (usually 2.5 blocks each way from the given street, for a total interval of about a quarter of a mile). The numbers in between on the x-axis are the major east-west streets (23rd, 34th, 42nd, etc.).
As the chart makes evident, there are five peak centers of change: the highest centered around 92nd Street, the second highest around 54th Street, the third around 75th Street, the fourth around 16th Street, and the fifth around 108th Street. There are three troughs of relatively low change density: the lowest around 61st Street, the next two, about equal, centered around 34th Street and around 99th Street.
A few conjectures: the 16th Street peak represents northward movement of gentrification from the former Meatpacking District, together with the emergence of Chelsea as the new art gallery district. The 54th Street peak represents a westward expansion of Midtown; the 75th Street peak may be a kind of second order "renewal" of this oldest part of the Upper West Side; the 92nd Street peak may, again, be a kind of second order renewal (perhaps due to an increased population density?); while the 108th Street peak is likely, in part, to be a southward and eastward expansion of the more upscale population drawn to Columbia University.
The 34th Street trough is explainable in part by the MTA railroad yards on the west side of the avenue below 33rd Street, the 61st Street trough by the public housing on the west side of the avenue and the Lincoln Center complex on its east side. The uptown trough may similarly be explained, at least in part, by the public housing there.
(These conjectures are very "off the top of my head" and, even if in some measure correct, do not pretend to address the underlying drivers of change in the city.)