This designation includes the 50 States and the District of Columbia.

The 48 contiguous States and the District of Columbia. Alaska, Hawaii, and outlying areas are excluded.

Information for the Commonwealth of Puerto Rico, the Virgin Islands of the United States, and Guam is published in the reports of the censuses of agriculture, population, housing, business, manufacturers, and mineral industries. In addition, some census of population and housing reports show information for the Canal Zone and American Samoa. Population and housing totals are also available for the small outlying areas of Midway, Wake, Canton and Enderbury Islands, Johnston Island and San Island, the Swan Islands the Corn Islands, and the Trust Territory of the Pacific Islands.

In Alaska there are no counties; for this State, census statistics were shown in 1960 for 24 election districts. Statistics for 1970 are presented for the 10 boroughs and 29 census divisions which generally conform to the 1960 election districts outside of the boroughs.

Areas established to provide tabulations useful in analyzing the population growth of SMSAs near coasts, lakes and rivers. Water locations first appeared in the 1960 population census report titled Standard Metropolitan Statistical Areas, PC(3)-1D.

These are essentially single SMSAs or clusters of SMSAs selected to represent relatively large but geographically compact concentrations of industrial activity. They are utilized in some reports from the census of transportation. There are 25 of these areas.

Twenty of these units (defined by a Federal interagency committee) are recognized in a subject report from the census of manufactures, Water Use in Manufacturing. Each region is a combination of counties grouped to recognize major drainage basins.

Ten of these (defined by the Department of the Interior) have statistics printed in the report from the 1963 Census of Commercial Fisheries.

Statistics for 8 of these regions are presented in a report from the census of business on one of the whole sale trade businesses. They are defined by the Departments of Defense and the Interior and by the Executive Office of the President.

Statistics for the 10 regions are shown in the annual Current Industrial Report, Lumber Production and Mill Stocks.

Statistics for the areas for brick and structural clay tile (except surfacing tile) appear in the monthly Current Industrial Report Clay Construction Products.

These regions are located in Louisiana, Texas, and New Mexico. In Louisiana, they are composed of parishes, and in New Mexico and Texas they are composed of counties. Statistics for the 17 districts are shown in the reports on petroleum and natural gas industries in the census of mineral industries.

This term applies to a unit of tabulation appearing in file B of the First Count summary tape, MCD-places occur in the following situations in most States, the incorporated places form sub-units within minor civil divisions in which they are located; in other States, all or some of the incorporated places are themselves also minor civil divisions; and incorporated places, as well as unincorporated places, may be located in two or more minor civil divisions. An MCD-place is, therefore, any place which is either tabulated in segments, if the place straddles MCD boundaries, or tabulated as a whole, if the place is an MCD itself or a sub unit of an MCD.

These are political units incorporated as cities, boroughs (excluding Alaska), villages, or towns (excluding New England States, New York, and Wisconsin). Most incorporated places are subdivisions of the minor civil divisions in which they are located; for example, an incorporated village located in an unincorporated township. Some incorporated places, however, constitute MCDs or cross MCD and county lines. Incorporated places never cross State lines since they are chartered by a State. In 1960, they numbered over 18,000.

Statistics for incorporated places of all types and sizes are given in the population and housing census reports; the figures for larger cities are quite detailed. The other censuses provide information for incorporated places of larger than a specified size:

2,500 in the census of governments and the retail trade and selected services segments of the census of business

5,000 in the wholesale trade segment of the census of business

10,000 in the census of manufactures.

In the census of business reports, statistics are shown for towns in New England and townships in Pennsylvania and New Jersey (not usually classified as incorporated places) with an urban population of 2,500 or more (5,000 for the wholesale trade segment) or a total population of 10,000 or more.

In the 1970 Census of Population and Housing, boroughs in Alaska are not included as incorporated places because they may include incorporated places within their limits and also they may include large areas with little population. Similarly excluded are towns in New England, New York, and Wisconsin. All townships are excluded.

Areas annexed to incorporated places of 2,500 or more inhabitants since the preceding census are recognized separately in certain decennial census tabulations. A one-digit annexation code on the summary tapes indicates areas annexed to cities since the previous census; 0 no and 5 = yes. A code 9 is used in some instances to identify areas annexed to smaller cities.

These are densely settled population centers which are not incorporated. Each has a definite residential nucleus, and boundaries are drawn by the Census Bureau to include insofar as possible, all the closely settled area. In the publications of the census of population and housing, statistics are shown, in all except urbanized areas, for unincorporated places of 1,000 or more population. In 1960, there were over 1,500 of these unincorporated places.

In order to recognize all unincorporated places of 1,000 or more outside the urbanized area, in unincorporated places are being enumerated separately in 1970 for settlements estimated to have at least 800 inhabitants, as was done in 1960. The Bureau has received varying degrees of cooperation from all the State highway departments in identifying and delineating these places and in providing maps; the coverage, therefore, should be more complete than ever before.

There will be no urban by special rule towns in New England or townships in New Jersey or Pennsylvania, as there were in the 1960 census. Unincorporated places may, instead, be defined for the built-up areas in any of these towns and townships which fall outside the urbanized areas.

Within the urbanized areas, except in New England, only unincorporated places of 5,000 inhabitants or more are recognized, in contrast to the 10,000 cutoff level in 1960. Census tract committees have aided greatly in extending the identification of these unincorporated places.

One further change, made with the consent of the Department of Defense, is to recognize and delineate military installations outside incorporated places; the parts of the installations that are built-up, are recognized as unincorporated places.

This designates all incorporated and unincorporated places of 2,500 or more. In 1960, towns in New England and townships in New Jersey and Pennsylvania, which contained no incorporated municipalities, had 25,000 or more inhabitants, or had from 2,500 to 25,000 inhabitants with a population density of 1,500 or more persons per square mile, were regarded as urban places; also included were counties in other States which contained no incorporated municipalities and had a density of 1,500 inhabitants or more per square mile. These special rules will not be applied in the 1970 census. There were almost 5,500 urban places in 1960 and will be over 6,000 in 1970.

An urbanized area contains at least one city which had 50,000 inhabitants in the census as well as the surrounding closely settled incorporated and unincorporated areas that meet the criteria for urban fringe areas. (There are a few urbanized areas where there are twin central cities that have combined population of at least 50,000. ) All persons residing in an urbanized area are included in the urban population.

In addition to its central city or cities, an urbanized area also contains the following types of contiguous areas, which together constitute its urban fringe:

A. Incorporated places with 2,500 inhabitants or more,
B. Incorporated places with less than 2,500 inhabitants, provided each has a closely settled area of 100 dwelling units or more.
C. Enumeration districts in unincorporated areas with a population density of 1,000 inhabitants or more per square mile. (The area of large nonresidential tracts devoted to such urban land uses as railroad yards, factories, and cemeteries is excluded in computing the population density.)
D. Other enumeration districts in unincorporated territory with lower population density provided that it serves one of the following purposes:
1. To eliminate enclaves
2. To close indentations in the urbanized area of one mile or less across the open end.
3. To link outlying enumeration districts of qualifying density that were no more than 1- 1/2 miles from the main body of the urbanized area.

A change in the definition since 1960 involves dropping the use of towns in the New England States, townships in ' New Jersey and Pennsylvania, and counties elsewhere which were classified as urban by special rule. These areas or their parts, will qualify as part of the urbanized area only if they meet rule C above.

The concept of an SMSA has been developed in order to present general-purpose statistics. On the basis of the criteria listed below, the geographical boundaries of SMSAs are drawn by the Office of Statistical Policy in the Bureau of the Budget with the advice of representatives of the major Federal statistical agencies. A four-digit code identifies each SMSA. These codes are defined in Federal Information Processing Standard Publications, No. 8.

In 1960, there were 215 SMSAs in the United States and Puerto Rico; as of 1969, there are 233. Generally speaking an SMSA consists of a county or group of counties containing at least one city (or twin cities) having a population of 50,000 or more plus adjacent counties which are metropolitan in character and are economically and socially integrated with the central city. In New England, towns and cities rather than counties are the units used in defining SMSAs. The name of the central city or cities is used as the name of the SMSA. See Figure 2. There is no limit to the number of adjacent counties included in the SMSA as long as they are integrated with the central city nor is an SMSA limited to a single State; boundaries may cross State lines, as in the case of the Washington, D. C. - Maryland - Virginia SMSA.

Where the Current Population Reports series presents statistics for the metropolitan and nonmetropolitan populations, metropolitan refers to persons residing in SMSAs and nonmetropolitan refers to persons not residing in an SMSA even though they may live in a city.

Criteria for SMSAs:

A. Population size -- each SMSA must include at least:
1. One city with 50,000 inhabitants or more, or
2. Two cities having contiguous boundaries and constituting, for general economic and social purposes, a single community with a combined population of at least 50,000, the smaller of which must have a population of at least, 15,000. If two or more adjacent counties each have a city of 50,000 inhabitants or more and the cities are within 20 miles of each other (city limits to city limits), they will be included in the same area unless there is definite evidence that the two cities are not economically and socially integrated.
B. Metropolitan character of outlying counties- - specifically, the following criteria must be met:
1. At least 75 percent of the labor force of the county must be in the nonagricultural labor force.
2. The county must meet at least one of the following conditions:
a. It must have 50 percent or more ofits population living in contiguous minor civil divisions having a density of at least 150 persons per square mile, in an unbroken chain of minor civil divisions with such density radiating from a central city in the area.
b. The number of nonagricultural workers employed in the county must equal at least 10 percent of the number of nonagricultural workers employed in the county containing the largest city in the area, or the outlying county must be the place of employment of at least 10,000 nonagricultural workers.



c. The nonagricultural labor force living in the county must equal at least 10 percent of the nonagricultural labor force living in the county containing the largest city in the area, or the outlying county must be the place of residence of a nonagricultural labor force of at least 10,000.
C. Integration of central county and outlying counties-- sufficient economic and social communication:
1. At least 15% of the workers living in the given outlying county must work in the county or counties containing the central city or cities of the area, or
2. At least 25 percent of those working in the given outlying county must live in the county or counties containing the central city or cities of the area.
D. In New England, where city and town are administratively more important than the county and data are compiled locally for those minor civil divisions, cities and towns are the units used in defining SMSAs. Here, a population density criterion of at least 100 persons per square mile is used as the measure of metropolitan character and the integration criteria for the towns and cities are similar to criterion C.

The largest city in an SMSA is always a central city. One or two additional cities maybe secondary central cities in the SMSA on the basis and in the order of the following criteria:

A. The additional city or cities must have a population of one-third or more of that of the largest city and a minimum population of 25,000 except that both cities are central cities in those instances where cities quality under A, (2) of the criteria for SMSAs.
B. The additional city or cities must have at least 250,000 inhabitants.

The ring is all of the SMSA that is not part of the central city itself. This concept is used in the population census to provide information on commuting patterns of workers. Reports from the 1970 census will include all existing SMSAs. Boundries will not be re-drawn until 1972.

In 1960, cities with a population of 1 million or more identified groups of tracts to form special areas for population and housing tabulations: Chicago - Community Areas; Detroit - Sub-community Areas; Los Angeles - Statistical Areas; New York - Health Areas; Philadelphia - Wards. No such areas will be identified in 1970 tabulations.

The side of a city block; a segment of the periphery of a block or of a cul-de-sac into a block. Block faces can be identified using the Address Coding Guide and grouped to any specifications at request for a special tabulation.

This designation is new in 1970, and is used in census-by-mail areas where Address Coding Guides have been prepared. A block group is a combination of contiguous blocks having a combined average population of about 1,000. Block groups are approximately equal in area (discounting parks, cemeteries, railroads yards, industrial plants, rural areas, etc.); they are subdivisions of census tracts which simplify numbering and data control. Each block group is identified by the first digit of the three-digit block number. Block group 1 will contain any block in range 101-199, block group 2 in range 201-299, etc. However, normally only the first few numbers in a range are used. For purposes of providing small-area population and housing census data, they are the equivalent of enumeration districts within the mail-out/mail-back areas where Address Coding Guides have been prepared. Block groups (and blocks) are typically defined without regard to the boundaries of political or administrative areas, such as cities, minor civil divisions, and congressional districts. When a block group straddles one or more of these boundaries, data for those parts in different areas will be tabulated separately. Where such a split occurs, the tapes contain two (or more) data records having the same block group number within the census tract but a different place, annexation, minor civil division, or congressional district code depending on the situation. The First Count tapes do not contain a flag to indicate that a block group has been split; however, the Master Enumeration District List (MEDList) can be used to identify split block groups.

In the Address Coding Guide areas, block groups are actually split into so-called computer enumeration districts by the Census Bureau to facilitate data processing and enumeration follow-up. No tabulations are produced for these so called enumeration districts since they cannot be mapped as coherent geographic entities.

In untracted areas where city blocks will be tabulated on a contract basis, blocks have been numbered in block numbering areas which are identified by census tract-type numbers ranging from 9400.00 to 9999.00. Block numbering areas are also defined in parts of untracted counties that are within the 1970 potential urbanized area. Block numbering areas are unique within county boundaries and usually contain a population of about 4,000 people. Data are not tabulated for these areas.

Population and housing data from the decennial censuses have been published in a series of separate reports by census tract (primarily for SMSAs); a great many more statistics will be tabulated but not published and will be available at a nominal cost from the 1970 censuses.

Information about the census tract program is found in the Census Bureau's Census Tract Manual which tells how to get tracts established, outlines the responsibilities of local groups, tells about the large body of published and unpublished statistics which the Bureau has tabulated for census tracts, and reviews the ways tract statistics have been made more useful.

Temporary offices are set up in each of the Census Bureau's regional field office areas, the number for each area being determined primarily by the size and character of the population. Under the direction of the District Supervisor, crew leaders and their enumerators are selected and trained, and a all follow-up work is carried out. Incomplete forms are completed and non-responses are eliminated if possible. For control purposes, each of the approximately 400 District Offices has been assigned a four-digit numeric code. The first two digits indicate the Census Field Region and the two remaining ones the specific District Office within the Region. The District Office boundaries contain about one-half million people and may cross State lines.

In the ACG, the lowest and highest addresses of a range of addresses on a block face. Both are odd or even, never mixed except through error. In most cases the potential address range is shown. An address range of zero (0) to zero may appear when a block side contains no addresses or the potential range is unknown. High and low addresses may be the same if there is only one address on a block face.

During the preparation of ACGs, a three-digit numeric code, known as the area code, was devised solely to provide an identification combining MCD and place codes. The area code was assigned to MCDs or CCDs alphabetically within county, and to all places within each MCD or CCD. Numbers were assigned at intervals of five, beginning with 005, (except in Cook County, Illinois and Allegheny County, Pennsylvania, where numbers were assigned at intervals of four, beginning with 004) to provide for insertion of new places and changes in alphabetic listing of MCD/CCDs. The MCD-place combination would have required seven digits if the normal codes were used.

Generally a five-digit identifier of a single record in the Address Coding Guide for an urbanized area. The serial number is unique within SMSA.

A suffix to the serial number, known as the check digit, is mathematically derived from the serial number and used to detect errors in transcribing or punching serial numbers. A typical use of the serial number is to identify records that are to be changed. When the serial number and its check digit are introduced into the computer (with other data), the check digit is recomputed and compared to that supplied. In the absence of a match, the entire record is rejected for correction of the error.

A five-digit numeric code for each street name in the Address Coding Guide. The street code is unique within postal finance areas. The postal finance area number (identification used by the Post Office Department) is the last 5-digits of the 7-digit Postal Data Code. The first two digits are a numeric State code. Postal Data Codes must be used with the street codes to distinguish among identical street codes in different postal finance areas.

Some portions of SMSAs enumerated by the mail-out/mail-back procedure are not covered by the purchased mailing list. The Census Bureau made its own pre-listing of addresses in these areas. Mailing pieces for these areas were addressed by hand. There are no plans to add these addresses onto the computerized Address Register.

Contains relevant geographic codes and place names for the political and statistical subdivisions of States for which 1970 census data are tabulated. The MEDList is an expanded version of the 1960 Geographic Identification Code Scheme. The smallest unit on the MEDList is the block group in areas where Address Coding Guides have been developed and the enumeration district in all other areas. The MEDList contains a total population and housing unit count for each block group and enumeration district. The MEDList is needed in conjunction with the census use summary tapes and microfilm.

This file lists all 35,000 U.S. post offices and the names of cities and towns within each (including variant names and spellings). The ZIP codes, 3-digit codes for multi-ZIP code post offices, and 5-digit codes for single ZIP code post offices, are included for each place name. The total file consists of over 100,000 records and is used for ZIP coding of incoming addresses which do not contain ZIP codes; it is available on request at cost.

This computer tape or printed listing of street names within post office area includes street codes and number ranges within ZIP code. It can be used to assign 5-digit ZIP codes to addresses with missing ZIP codes and for assigning street codes. Since this file contains no confidential information, it can be made available to the public on a cost basis.

Alphanumeric fields on the summary tapes which contain various geographic identifiers as determined by the designated summary area. These keys appear on various summary tapes for publication control purposes. Refer to the technical documentation of summary tapes for further details.