A structure is defined as a separate building that either has open space on all four sides, or is separated from other structures by dividing walls that extend from ground to roof.

Statistics are presented in terms of the number of housing units rather than the number of residential structures. However, the number of structures for the first two categories may be derived. For 1-unit structures (which include trailers), the number of housing units and the number of structures are the same. For 2- unit structures, the number of housing units is twice the number of structures. For the remaining categories, the number of structures cannot be derived from the data as tabulated.
The categories for number of housing units in the structure in 1960 are not directly comparable with those in 1950, particularly for 1- and 2-unit structures. In the 1950 tract report, units in detached or attached structures were shown separately but those in semidetached structures containing 1 or 2 units were combined into one category. Comparability between 1950 and 1960 data may else be affected by the change in concept from dwelling unit to housing unit.