Quick look at proportion of land within SF that is covered by a structure according to city building footprint data. This excludes interior courtyards, uncovered ground-level parking, ie everything without a roof.
Area measurements in square meters, excluding the bay and lakes (census tracts may include bodies of water, this compares only land area.)
Zoom in to see the census tract outline. Also, some of the numbered links are bad, if so try the 'unbroken link'.