A housing unit is vacant if no person were living in it at the time of enumeration. However, if its occupants were only temporarily absent, the unit was considered occupied. Units temporarily occupied by persons having a usual place of residence elsewhere were considered vacant (classified as not resident units in 1950).
Year-round vacant units are those intended for occupancy at any time of the year. Seasonal vacant units are those intended for occupancy during only a season of the year.

Available vacant units are those which arc on the market for year-round occupancy, are in either sound or deteriorating condition, and are offered for rent or for sale. The group for sale only is limited to available units for sale only and excludes units for rent or sale. The group for rent consists of units offered for rent and those-offered for rent or sale. The 1960 category available vacant is comparable with the 1950 category vacant nonseasonal not dilapidated, for rent or sale.

Othervacant units comprise the remaining vacant housing units. They include dilapidated units, seasonal units, units rented or sold and awaiting occupancy, units held for occasional use, and units held off the market for other reasons. This category is comparable with the 1950 category other vacant and nonresident.