To help get vacant commercial spaces filled in Evanston’s downtown area, the city is about to select small businesses to participate in a new retail incubator. What is Evanston’s commercial vacancy rate, and how is it determined? Commercial vacancy rates can be determined in more than one way. “Vacancy relief is what we would call a valuation tool that is available to be used by county assessors. Zalmezak said there has been some talk about including vacant commercial buildings in Evanston’s registry, but no action so far.