Hypothesis: That the likelyhood of any given homeowner shoveling their sidewalks increases if their neighbor on either side shovels their sidewalk. This increased desire to shovel is prompted by guilt, envy, and the lessening of perceived physical, emotional, and climactic barriers to snow shoveling.
For example, if the neighbors on either side of Citizen A are out of town during a snow event, and fail to shovel their sidewalk, Citizen A will be 25% more unlikely to shovel his/her sidewalks. However, if the two ajacent neighbors of Citizen A are not only in town, but diligent and timely in their sidewalks shoveling, starting immediately at the cease of snowfall and shoveling from "edge to edge," Citizen A will be twice as likely to shovel his/her sidewalk in a timely manner.
This is called the Shoveling-Joneses effect.
Impact: If this hypothesis is true, any given block of sidewalks ought to behave as a unit, with neighbor-to-neighbor S-J effects creating areas of show-shovelled continuity. Any given block, depending on the density of initial likelihood to shovel, will become either a shoveled or an unshoveled blocks. The city would, in this case, act as a self-reinforcing positive feedback mechanism. Sidewalks would, from the air, become a quilt of white and gray, as block-by-block, sidewalks are shoveled or left to melt, as is their wont.