Standard metropolitan statistical area (SMSA).-Except in New England, an SMSA is a county or group of contiguous counties which contains at least one city of 50,000 inhabitants or more, or "twin cities" with a combined population of at least 50,000, the smaller of which must have at least 15,000. In addition to the county, or counties, containing such a city or cities, contiguous counties are included in an SMSA if, according to certain criteria, they are essentially metropolitan in character and are socially and economically integrated with the central city. In New England, SMSA's consist of towns and cities, rather than counties.

The definition of SMSA's used in the quarterly surveys is being updated to reflect the 243 areas designated SMSA's in the 1970 census, recognized by the Office of Management and Budget, as of February 1971. The 1972 statistics presented in this report for inside SMSA's, inside central cities, outside central cities and outside SMSA's are based partially on the 1960 census definitions and partially on the 1970 census definitions. For the identification of the 243 SMSA's and their constituent parts, refer to the 1970 Housing Census Series HC(1)A or HC(1)B reports or to the 1970 Population Census Series PC(1)- A, B, or C reports. The statistics for inside SMSA's and outside SMSA's presented for the year 1971 relate to the areas (212) designated SMSA's at the time of the 1960 census. For a list of the 212 SMSA's and their constituent parts, refer to the individual chapters (or Series HC(1) reports) in the 1960 Census of Housing, Volume I, States and Small Areas; to the 1960 Census of Population, Volume I, Number of Inhabitants.

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Housing unit. -- Beginning with the second quarter 1960, the 1960 census housing unit concept was used to enumerate separate living quarters. Prior to that time, separate living quarters were enumerated according to the 1950 dwelling unit definition. The major difference between the two is not in content but in sharpening of the criteria by which separate units are identified. It is expected that the housing unit concept will yield. better coverage of both occupied and vacant living quarters than the dwelling unit concept. Although no statistical measure of the effect of the change is available at this time, it is believed to be too small to affect the vacancy rates.

A group of rooms or a single room is regarded as a housing unit when it is occupied as separate living quarters, that is, when the occupants do not live and eat with any other persons in the structure, and there is either (1) direct

access from the outside or through a common hall, or (2) a kitchen or cooking equipment for the exclusive use of the occupants.

Vacant living quarters intended for occupancy as separate living quarters and those that meet the physical criteria defined above are separate housing units. Because it is customary in some localities for occupants to furnish their own cooking equipment, vacant units without a kitchen or cooking equipment are considered to have such equipment if the last occupants had cooking equipment.

Living quarters of the following types are excluded from the housing unit inventory: Dormitories, bunkhouses, and barracks; quarters in predominantly transient hotels, motels, and the like, except those occupied by persons who consider the hotel their usual place of residence; quarters in institutions, general hospitals, and military installations except those occupied by staff members or resident employees who have separate living arrangements.

Quarters for roomers or boarders having shared living arrangements are excluded from the housing inventory if there are five or more such rooms; they are combined as one housing unit if there are four or fewer such rooms.

Trailers, tents, and boats are excluded if vacant, used for business, or used for extra sleeping space or vacations.

Dwelling unit, 1950.--The 1950 dwelling unit was defined as follows: A group of rooms occupied as separate living quarters was a dwelling unit if it had separate cooking equipment or if it constituted the only living quarters in the structure. Each apartment in a regular apartment house was a dwelling unit even though it may not have had separate cooking equipment. Apartments in residential hotels were dwelling units if they had separate cooking equipment or consisted of

two or more rooms.

Vacant quarters intended for occupancy as separate living quarters and meets the physical criteria defined above were separate dwelling units. Vacant units were considered as having cooking equipment if they were equipped with such equipment or if the last occupants had cooking equipment.

In general, living quarters of the types excluded from the housing unit inventory were excluded from the dwelling unit inventory.

Occupied housing units.-- A housing unit is occupied if a person or group of persons was living in it at the time of enumeration or if the occupants were only temporarily absent, as for example, on vacation. The persons living in the unit must consider it their usual place of residence or have no usual place of residence elsewhere. The count of occupied housing units is the same as the count of households.

Units occupied by persons with usual residence elsewhere.--A housing unit which is occupied temporarily by persons who usually live elsewhere is enumerated as a vacant unit provided the usual place of residence is held for the household and is not offered for rent or for sale. For example, a beach cottage occupied at the time of enumeration by a family which has a usual place of residence in the city is included in the count of vacant units. Their house in the city would be reported "occupied" and would be included in the count of occupied units since the occupants are only temporarily absent.

Units occupied by persons with usual residence elsewhere are included with seasonal units or with year-round vacant units in the category "Held off market."

Vacant housing units. --A housing unit is vacant if no one is living in it at the time of enumeration, unless its occupants are only temporarily absent. In addition, a vacant unit may be one which is entirely occupied by persons who have a usual residence elsewhere.

New units not yet occupied are classified as vacant housing units if construction has reached a point where all exterior windows and doors are installed and final usable floors are in place. Vacant units are excluded if unfit for human habitation, that is, the roof, walls, windows or doors no longer protect the interior from the elements, or if there is positive evidence (such as a sign on the house or in the block) that the unit is to be demolished or is condemned. Also excluded are quarters being used entirely for nonresidential purposes, such as a store or an office, or quarters used for the storage of business supplies or inventory, machinery, or agricultural products.

Vacant sleeping rooms in lodginghouses, transient accommodations, barracks, and other quarters not defined as housing units are not included in the statistics in this report. (See section on "Housing unit.")

Year-round vacant units.--Year-round units are those intended for occupancy at any time of the

year, even though they may not be in use the year round. In resort areas, a housing unit which is usually occupied on a year-round basis was considered a year-round unit. On the other hand, a housing unit located in the closely built-up area of a nonresort city was considered a "year-round" unit even though it may be occupied only part of the year. As indicated above, year-round units temporarily occupied by persons with usual residence elsewhere are included with year-round vacant units.

Year-round vacant units are classified in the following categories:

Vacant units for rent. --This group consists of vacant units offered for rent and those offered for rent or sale. In the reports published before 1972 vacant units "available for rent" consisted of vacant units offered for rent and those offered for rent or sale which were rated as being in sound or deteriorating condition; units rated as dilapidated were excluded.

Vacant units for sale only. --This group is limited to units for sale only; it excludes units for rent or sale. In the reports published before 1972 vacant units "available for sale" consisted of units for sale only which were rated as being in sound or deteriorating condition; units rated as dilapidated were excluded.

If a unit was located in a multiunit structure which was for sale as an entire structure and if the unit was not for rent, it was reported as "held off market." However, if the individual unit was intended to be occupied by the new owner, it was reported as "for sale."

Vacant units rented or sold.--This group consists of year-round vacant units which have been rented or sold but the new renters or owners have not moved in as of the day of enumeration. In the reports published before 1972 this group was limited to units rated "sound or deteriorating."

Vacant units held off the market.--Included in this category are year-round units which were vacant for reasons other than those mentioned above: For example, held for occupancy of a caretaker, janitor, and the like; held for settlement of estate; held for personal reasons of the owner; and temporarily occupied by persons who have a usual place of residence elsewhere. In the reports published before 1972 the category was limited to units which were rated "sound or deteriorating."

Seasonal vacant units.--Seasonal housing units are those intended for occupancy during only a season of the year and are found primarily in