Housing units comprise houses, apartments, groups of rooms, or single rooms, which are occupied, or vacant but intended for occupancy, as separate living quarters. Specifically, there is a housing unit when the occupants live and eat separately from any other persons in the structure and there is either (1) direct access to the unit from the outside or through a common hall, or (2) in 1960, a kitchen or cooking equipment for the occupants exclusive use: in 1970, complete kitchen facilities for the occupants exclusive use.
Structures intended primarily for business or other non-residential use may contain housing units; for example, the living quarters of a merchant in back of his shop. Separate living quarters occupied by staff personnel (but not inmates) in institutions which meet the definitional criteria constitute housing units; as do separate living quarters of supervisory staff in dormitories, nursing homes, etc. Any separate living quarters, which meet the above criteria, in rooming or boarding houses are classified as housing units, as are entire rooming or boarding houses where there are four or fewer roomers unrelated to the person in charge. Trailers, tents, boats, railroad cars, hotel and motels occupied by usual residents which meet the definitional criteria constitute housing units; as do vacant rooms or suites in hotels where 75 percent or more of the accommodations are occupied by usual residents.

Ascertained for all persons 14 years of age and over for the preceding calendar year, even if they had no income. Total income is the sum of the dollar amounts of money respondents reported receiving (best estimate if exact amount not known) as wages or salary income, net nonfarm and farm self-employment income, and other income, as specified below. In statistics on family income or household income, the combined incomes of all members of each family or household are treated as a single amount. For unrelated individual income and for income statistics of persons 14 years and over, the classification is by the amount of their own (individual) total income.

Income is tabulated by several intervals. For example, under $1,000, $1,000- $1,999... $9,000-$9,999, $10,000-$14,999, $15,000- $24,999, $25,000 and over. The 1960 census basic records included dollar amounts for each type of income in intervals of $10 from $1-$9 to $9,990-$9,999 and in intervals of $1,000 from $10,000-$10,999 to $24,000-$24,999. Two separate categories were provided for each of the following items: (1) no income and (2) incomes of $25,000 and over. (Net loss from self-employment and all other sources was included in intervals of $100 from $1 - $99 to $9,800-$9,899. Net losses of $9,900 and over were tabulated separately.)

In the 1970 census basic records, for dollar amounts of each type of income, questionnaire dollar entries within $100 intervals from $1-$99, $100-$199, to $99,900- !$99,999 are shown as one-tenth of the midpoint value for that interval. For example, any questionnaire entry between $100 and $199 is represented as 15 on the basic record; any questionnaire entry between $99,900 and $99,999 is represented as 9995 on the basic record. Similarly, dollar amounts within $10,000 intervals from $100,000-$109,999, $110,000-$119,999 to $980,000-$989,999 are shown as one-tenth of the midpoint value for that interval. For example, any questionnaire entry between $100,000 and $109,999 is represented as 10500 on the basic record; any questionnaire entry between $980,000 and $989,999 is represented as 98500 on the basic record. Separate categories are provided for no income and incomes of $990,000 or more. Net losses from self-employment income (section 104.12 below) and income from all other sources (section 104.23 below) are included in intervals of $100 from $1-$99 to $9,800-$9,899. Net losses of $9,900 or more are carried as one category.

Median and mean incomes are calculated for families, unrelated individuals, and persons 14 years and over for total income and for each type of income. (In the 1960 derivation of aggregate amounts for calculating mean income, persons in the open-ended interval $25,000 and over were assigned an estimated mean of $50,000 for each income type. In the 1970 derivation of aggregate amounts for each income type, persons in the open-ended interval $990,000 and over are assigned an estimated mean of $995,000.)