Vast undercount -- probably for every city. Commercial financing has convenants which require minimum occupancy, landlords are heavily incentivized to keep tenants on the books even if they're not actually using the space.

Know personally of startups in SF which have been discouraged from cutting their lease and paying a penalty so that the landlord can keep occupancy #s high. Of course, there are sweeteners involved to keep them "occupying" the space when in reality they moved out >6 months ago. They'll be in the space for years to come...