APPENDIX A. Area Classifications CONTENTS Area Measurement A- 1 Barrio (See Municipio Subdivision) Barrio-Pueblo (See Municipio Subdivision) Block A-2 Block Group (BG) A-2 Block Numbering Area (BNA) (See Census Tract and Block Numbering Area) Boundary Changes A-2 Census Block (See Block) Census Code (See Geographic Code) Census Designated Place (CDP) (See Place) Census Geographic Code (See Geographic Code) Census Region and Census Division A-2 Census Tract and Block Numbering Area A-2 Central City (See Metropolitan Area) Central Place (See Urbanized Area) Comunidad (See Place) Congressional District A-3 Consolidated Metropolitan Statistical Area (CMSA) (See Metropolitan Area) Crews of Vessels (See Area Measurement, see Block, see Census Tract and Block Numbering Area) Election District (See Voting District) Farm (See Urban and Rural) Federal Information Processing Standards (FIPS) Code (See Geographic Code) Geographic Block Group (See Block Group) Geographic Code A-3 Geographic Presentation A-4 Hierarchical Presentation (See Geographic Presentation) Historical Counts A-4 Internal Point A-4 Inventory Presentation (See Geographic Presentation) Land Area (See Area Measurement) Latitude (See Internal Point) Longitude (See Internal Point) Metropolitan Area A-5 Metropolitan Statistical Area (MSA) (See Metropolitan Area) Municipio A-5 Municipio Subdivision A-6 Outlying Areas of the United States (See State, see United States) Place A-6 Population or Housing Unit Density A-6 Precinct (See Voting District) Primary Metropolitan Statistical Area (PMSA) (See Metropolitan Area) Puerto Rico (See State) Rural (See Urban and Rural) State A-6 Subbarrio (See Municipio Subdivision) Tabulation Block Group (See Block Group) TIGER A-6 Tract (See Census Tract and Block Numbering Area) United States A-7 Urban and Rural A-7 Urbanized Area A-7 Voting District (VTD) A-8 Water Area (See Area Measurement) Zona Urbana (See Place) These definitions are for all geographic entities and concepts that the Census Bureau will include in its standard 1990 census data products for Puerto Rico. Not all entities and concepts are shown in any one 1990 census data product. For a description of geographic areas, see appendix F in this documentation. AREA MEASUREMENT Area measurements provide the size, in square kilometers (also in square miles in printed reports), recorded for each geographic entity for which the Census Bureau tabulates data in general-purpose data products (except crews-of-vessels entities). (Square kilometers may be divided by 2.59 to convert an area measurement to square miles.) Area was calculated from the specific set of boundaries recorded for the entity in the Census Bureau's geographic data base (see "TIGER"). On machine-readable files, area measurements are shown to three decimal places; the decimal point is implied. In printed reports and listings, area measurements are shown to one decimal. The Census Bureau provides measurements for both land area and total water area for the 1990 census; the water figure for Puerto Rico includes inland, coastal, and territorial water. (For the 1980 census, the Census Bureau provided area measurements for land and inland water.) The Census Bureau will provide measurements for the component types of water for the affected entities in a separate file. "Inland water" consists of any lake, reservoir, pond, or similar body of water that is recorded in the Census Bureau's geographic data base. It also includes any river, creek, canal, stream, or similar feature that is recorded in that data base as a two-dimensional feature (rather than as a single line). The portions of the ocean, related large embayments, and the Caribbean Sea that belong to the United States and its territories are considered to be "coastal" and "territorial" water. Rivers and bays that empty into these bodies of water are treated as "inland water" from the point beyond which they are narrower than one nautical mile across. Identification of land and inland, coastal, and territorial waters is for statistical purposes, and does not necessarily reflect legal definitions thereof. By definition, census blocks do not include water within their boundaries; therefore, the water area of a block is always zero. Land area measurements may disagree with the information displayed on census maps and in the TIGER File because, for area measurement purposes, features identified as "intermittent water" are reported as land area. For this reason, it may not be possible to derive the land area for an entity by summing the land area of its component census blocks. In addition, the water area measurement reported for some geographic entities includes water that is not included in any lower-level geographic entity. Therefore, because water is contained only in a higher-level geographic entity, summing the water measurements for all the component lower-level geographic entities will not yield the water area of that higher-level entity. This occurs, for example, where water is associated with a municipio subdivision but is not assigned to any census tract. Crews-of-vessels entities (see "Census Tract and Block Numbering Area" and "Block") do not encompass territory and therefore have no area measurements. The accuracy of any area measurement figure is limited by the inaccuracy inherent in (1) the location and shape of the various boundary features in the data base, and (2) rounding affecting the last digit in all operations that compute and/or sum the area measurements. BLOCK Census blocks are small areas bounded on all sides by visible features such as streets, roads, and streams and by invisible boundaries such as municipio and barrio limits, property lines, and short, imaginary extensions of streets and roads. Tabulation blocks, used in census data products, are in most cases the same as collection blocks, used in the census enumeration. In some cases, collection blocks have been "split" into two or more parts required for data tabulations. Tabulation blocks do not cross the boundaries of municipios, municipio subdivisions, places, census tracts or block numbering areas, voting districts, urban or rural areas, or urbanized areas. The 1990 census is the first for which all of Puerto Rico is block-numbered. Blocks are numbered uniquely within each census tract or BNA. A block is identified by a three-digit number, sometimes with a single alphabetical suffix. Block numbers with suffixes generally represent collection blocks that were "split" in order to identify separate geographic entities that divide the original block. For example, when a barrio boundary runs through data collection block 101, the data for the portion inside one barrio is tabulated in block 101A and the portion in the other barrio, in block 101B. A block number with the suffix "Z" represents a "crews-of-vessels" entity for which the Census Bureau tabulates data, but that does not represent a true geographic area; such a block is shown on census maps associated with an anchor symbol and a census tract or block numbering area with a .99 suffix. Some block group records may not have any block numbers associated with them; this occurs where the entire area of the block group consists only of water. BLOCK GROUP (BG) Geographic Block Group A geographic block group (BG) is a cluster of blocks having the same first digit of their identifying numbers within a census tract or block numbering area (BNA). For example, BG 3 within a census tract or BNA includes all blocks numbered between 301 and 397. In most cases, the numbering involves substantially fewer than 97 blocks. Geographic BG's never cross census tract or BNA boundaries, but may cross the boundaries of municipio subdivisions, places, urbanized areas, and voting districts. BG's generally contain between 250 and 550 housing units, with the ideal size being 400 housing units. Local officials delineated BG's for the 1990 census using Census Bureau guidelines. Tabulation Block Group In the data tabulations, a geographic BG may be split to present data for every unique combination of municipio subdivision, place, urbanized area, voting district, and urban/rural shown in the data product; for example, if BG 3 is located in two barrios, there will be separate tabulated records for each portion of BG 3. BG's are used in tabulating decennial census data throughout Puerto Rico for the 1990 census, but only in block-numbered areas for the 1980 census. For purposes of data presentation, BG's are a substitute for the enumeration districts (ED's) used for reporting data in many parts of Puerto Rico for the 1980 census and throughout Puerto Rico for pre-1980 censuses. BOUNDARY CHANGES The boundaries of some places changed from those reported for the 1980 census. The historical counts shown for places are not updated for such changes, and thus reflect the population and housing units in the area as delineated at each census. Boundary changes are not reported for statistical areas. CENSUS REGION AND CENSUS DIVISION For statistical purposes, the United States is divided into four census regions, which are further subdivided into nine divisions. Puerto Rico is not assigned to any region or division. CENSUS TRACT AND BLOCK NUMBERING AREA Block Numbering Area (BNA) Block numbering areas (BNA's) are small statistical subdivisions of a municipio for grouping and numbering blocks in municipios that do not have census tracts. The Puerto Rico Planning Board and the Census Bureau delineated BNA's for the 1990 census, using guidelines similar to those for the delineation of census tracts. BNA's do not cross municipio boundaries. BNA's are identified by a four-digit basic number and may have a two-digit suffix; for example, 9901.07. The decimal point separating the four-digit basic BNA number from the two-digit suffix is shown in printed reports, in microfiche, and on census maps; in machine-readable files, the decimal point is implied. Many BNA's do not have a suffix; in such cases, the suffix field is left blank in all data products. BNA numbers range from 9501 through 9989.99, and are unique within a municipio (numbers in the range of 0001 through 9499.99 denote a census tract). The suffix .99 identifies a BNA that was populated entirely by persons aboard one or more civilian or military ships. A "crews-of-vessels" BNA appears on census maps only as an anchor symbol with its BNA number (and block numbers on maps showing block numbers); the BNA relates to the ships associated with the onshore BNA's having the same four-digit basic number. Suffixes in the range .80 through .98 identify BNA's that either were revised or were created during the 1990 census data collection activities. Some of these revisions produced BNA's that have extremely small land area and may have little or no population or housing. For data analysis, such a BNA can be summarized with an adjacent BNA. Census Tract Census tracts are small, relatively permanent statistical subdivisions of a municipio. Census tracts in Puerto Rico are delineated for all metropolitan areas (MA's) and other highly populated municipios by the Puerto Rico Planning Board, in consultation with municipio officials and following Census Bureau guidelines. Census tracts usually have between 2,500 and 8,000 persons and, when first delineated, are designed to be homogeneous with respect to population characteristics, economic status, and living conditions. Census tracts do not cross municipio boundaries. The spatial size of census tracts varies widely depending on the density of settlement. Census tract boundaries are delineated with the intention of being maintained over a long time so that statistical comparisons can be made from census to census. However, physical changes in street patterns caused by highway construction, new development, etc., may require occasional revisions; census tracts occasionally are split due to large population growth, or combined as a result of substantial population decline. Census tracts are referred to as "tracts" in all 1990 data products. Census tracts are identified by a four-digit basic number and may have a two-digit suffix; for example, 6059.02. The decimal point separating the four-digit basic number from the two-digit suffix is shown in printed reports, in microfiche, and on census maps; in machine-readable files, the decimal point is implied. Many census tracts do not have a suffix; in such cases, the suffix field is left blank in all data products. Leading zeros in a census tract number (for example, 002502) are shown only on machine-readable files. Census tract numbers range from 0001 through 9499.99 and are unique within a municipio (numbers in the range of 9501 through 9989.99 denote a block numbering area). The suffix .99 identifies a census tract that was populated entirely by persons aboard one or more civilian or military ships. A "crews-of-vessels" census tract appears on census maps only as an anchor symbol with its census tract number (and block numbers on maps showing block numbers). These census tracts relate to the ships associated with the onshore census tract having the same four-digit basic number. Suffixes in the range .80 through .98 usually identify census tracts that either were revised or were created during the 1990 census data collection activities. Some of these revisions may have resulted in census tracts that have extremely small land area and may have little or no population or housing. For data analysis, such a census tract can be summarized with an adjacent census tract. CONGRESSIONAL DISTRICT Puerto Rico is represented in the U.S. House of Representatives by a nonvoting delegate, referred to as a "resident commissioner." GEOGRAPHIC CODE Geographic codes are shown primarily on machine-readable data products, such as computer tape and compact disc-read only memory (CD-ROM), but also appear on other products such as microfiche; they also are shown on some census maps. Codes are identified as "census codes" only if there also is a Federal Information Processing Standards (FIPS) code for the same geographic entity. A code that is not identified as either "census" or "FIPS" usually is a census code for which there is no FIPS equivalent or for which the Census Bureau does not use the FIPS code. The exceptions, which use only the FIPS code in census products, are municipio, congressional district, and metropolitan area (that is, metropolitan statistical area, consolidated metropolitan statistical area, and primary metropolitan statistical area). Census Code Census codes are assigned for a variety of geographic entities, including Puerto Rico, municipio subdivision, place, urbanized area, and voting district. The structure, format, and meaning of census codes appear in the 1990 census Geographic Identification Code Scheme and in the data dictionary portion of the technical documentation for summary tape files and CD-ROM's. Federal Information Processing Standards (FIPS) Code Federal Information Processing Standards (FIPS) codes are assigned for a variety of geographic entities, including congressional district, county (including statistically equivalent entities such as municipio), barrio-pueblo and barrio, metropolitan area, place, and State (including statistically equivalent entities such as Puerto Rico). The structure, format, and meaning of FIPS codes used in the census are shown in the 1990 census Geographic Identification Code Scheme and in the data dictionary portion of the technical documentation for summary tape files and CD-ROM's. The objective of the FIPS codes is to improve the use of data resources of the Federal Government and avoid unnecessary duplication and incompatibilities in the collection, processing, and dissemination of data. More information about the FIPS and FIPS code documentation is available from the National Technical Information Service, Springfield, VA 22161. United States Postal Service (USPS) Code The United States Postal Service (USPS) code for Puerto Rico is used in all 1990 census data products. The code is a two-character alphabetic abbreviation: PR. The code is the same as the FIPS two-character alphabetic abbreviation. GEOGRAPHIC PRESENTATION Hierarchical Presentation A hierarchical geographic presentation shows the geographic entities in a superior/subordinate structure in census products. This structure is derived from the legal, administrative, or areal relationships of the entities. The hierarchical structure is depicted in report tables by means of indentation, and is explained for machine-readable media in the discussion of file structure in the geographic coverage portion of the abstract in the technical documentation. An example of hierarchical presentation for Puerto Rico is the "standard census geographic hierarchy": block, within block group, within census tract or block numbering area, within place, within municipio subdivision, within municipio, within Puerto Rico. Graphically, this is shown as: Puerto Rico Municipio Municipio subdivision Place (or part) Census tract/block numbering area (or part) Block group (or part) Block Inventory Presentation An inventory presentation of geographic entities is one in which all entities of the same type are shown in alphabetical or code sequence, without reference to their hierarchical relationships. Generally, an inventory presentation shows totals for entities that may be split in a hierarchical presentation, such as place, census tract/block numbering area, or block group. An example of a series of inventory presentations is: Puerto Rico, followed by all the municipios, followed by all the places in Puerto Rico. Graphically, this is shown as: Puerto Rico Municipio "A" Municipio "B" Municipio "C" Place "X" Place "Y" Place "Z" HISTORICAL COUNTS Historical counts for total population and total housing units are shown in the 1990 CPH-2, Population and Housing Unit Counts report series. As in past censuses, the general rule for presenting historical data is to show historical counts only for single, continually existing entities. Stated another way, if an entity existed for both the current and preceding censuses, the tables show counts for the preceding censuses. Included in this category are entities of the same type (municipio, municipio subdivision, place) even if they had changed their names. The historical counts shown are for each entity as it was bounded at each census. In cases where an entity was formed since a preceding census, such as a new place, the symbol three dots "..." is shown for earlier censuses. The three-dot symbol also is shown for those parts of a place that have extended into an additional municipio or municipio subdivision since the preceding census. In some cases, population and housing unit counts for individual areas were revised since publication of the 1980 reports (indicated by the prefix "r"). In a number of tables of 1990 CPH-2, Population and Housing Unit Counts, 1980 counts are shown for aggregations of individual areas, such as the number, population, and housing unit counts of places in size groups, or urban and rural distributions. Revisions of population and housing unit counts for individual areas were not applied to the various aggregations. Therefore, it may not be possible to determine the individual areas in a given aggregation using the historical counts; conversely, the sum of the counts shown for individual areas may not agree with the aggregation. INTERNAL POINT An internal point is a set of geographic coordinates (latitude and longitude) that is located within a specified geographic entity. A single point is identified for each entity; for many entities, this point may approximate the geographic center of that entity. If the shape of the entity caused this point to be located outside the boundaries of the entity, it is relocated from the center so that it is within the entity. By definition, the internal point for a block cannot fall in a body of water. On machine-readable products, internal points are shown to six decimal places; the decimal point is implied. METROPOLITAN AREA The general concept of a metropolitan area (MA) is one of a large population nucleus, together with adjacent communities that have a high degree of economic and social integration with that nucleus. Some MA's are defined around two or more nuclei. The MA classification is a statistical standard, developed for use by Federal agencies in the production, analysis, and publication of data on MA's. The MA's are designated and defined by the Federal Office of Management and Budget, following a set of official published standards. These standards were developed by the interagency Federal Executive Committee on Metropolitan Areas, with the aim of producing definitions that are as consistent as possible for all MA's throughout the United States and Puerto Rico. An MA in Puerto Rico must contain either a place with a minimum population of 50,000 or a Census Bureau-defined urbanized area and a total MA population of at least 100,000. An MA comprises one or more municipios that have close economic and social relationships. An outlying municipio must have a specified level of commuting to the central municipio(s) and also must meet certain standards regarding metropolitan character, such as population density, urban population, and population growth, to be included in an MA. The territory, population, and housing units in MA's are referred to as "metropolitan." The metropolitan category is subdivided into "inside central city" and "outside central city." The territory, population, and housing units located outside MA's are referred to as "nonmetropolitan." The metropolitan and nonmetropolitan classification cuts across the other hierarchies; for example, there is generally both urban and rural territory within both metropolitan and nonmetropolitan areas. To meet the needs of various users, the standards provide for a flexible structure of metropolitan definitions that classify an MA either as a metropolitan statistical area (MSA), or as a consolidated metropolitan statistical area (CMSA) that is divided into primary metropolitan statistical areas (PMSA's). Documentation of the MA standards and how they are applied is available from the Secretary, Federal Executive Committee on Metropolitan Areas, Population Division, U.S. Bureau of the Census, Washington, DC 20233. Central City In each MSA and CMSA in Puerto Rico, the largest place and, in some cases, additional places are designated as "central cities" under the official standards. The largest central city and, in some cases, up to two additional central cities may be included in the title of the MA; there also may be central cities that are not included in an MA title. Consolidated and Primary Metropolitan Statistical Area (CMSA and PMSA) If an area that qualifies as an MA has more than one million persons, primary metropolitan statistical areas (PMSA's) may be defined within it. In Puerto Rico, PMSA's consist of a large urbanized municipio or cluster of municipios that demonstrates very strong internal economic and social links, in addition to close ties to other portions of the larger area. When PMSA's are established, the larger area of which they are component parts is designated a consolidated metropolitan statistical area (CMSA). Metropolitan Statistical Area (MSA) Metropolitan statistical areas (MSA's) are relatively freestanding MA's and are not closely associated with other MA's. Metropolitan Area Title and Code The title of an MSA contains the name of its largest central city and up to two additional place names, provided that the additional places meet specified levels of population, employment, and commuting. The title of a PMSA may contain up to three place names, as determined above, or up to three municipio names, sequenced in order of population. A CMSA title also may include up to three names, the first of which generally is the most populous central city in the area. The second name may be the first place or municipio name in the most populous remaining PMSA; the third name may be the first place or municipio name in the next most populous PMSA. A regional designation may be substituted for the second and/or third names in a CMSA title if such a designation is supported by local opinion and is deemed to be unambiguous and suitable by the Office of Management and Budget. The titles for all MA's in Puerto Rico also contain the name of the Commonwealth. Each MA is assigned a four-digit FIPS code in alphabetical order of all MA's. If the fourth digit of the code is a "2," it identifies a CMSA. Additionally, there is a separate set of two-digit codes for CMSA's, also assigned alphabetically. MUNICIPIO The primary political divisions of Puerto Rico are termed "municipios." The Census Bureau, for statistical purposes, treats a municipio as the equivalent of a county in the United States. Each municipio is assigned a unique three-digit FIPS code in alphabetical order within Puerto Rico. MUNICIPIO SUBDIVISION The Census Bureau recognizes barrios-pueblos and barrios as the primary legal subdivisions (minor civil divisions, or MCD's) of municipios. The barrios-pueblos replace the "pueblos" reported in previous decennial censuses. In agreement with the Puerto Rico government, the Census Bureau no longer includes ciudades in its data tabulations. Each municipio subdivision is assigned a three-digit census code in alphabetical order within municipio and a five-digit FIPS code in alphabetical order within Puerto Rico. Subbarrio Subbarrios in 23 municipios are legal subdivisions of the barrios-pueblos and some barrios. The Census Bureau presents the same types of 1990 census data for these "sub-MCD's" as it does for the barrios-pueblos and barrios. Each subbarrio is assigned a two-digit census code in alphabetical order within municipio and a five-digit FIPS code in alphabetical order within Puerto Rico. PLACE For the reporting of decennial census data, places in Puerto Rico consist of zonas urbanas and comunidades. Each place is assigned a four-digit census code and a five-digit FIPS code that are unique within Puerto Rico. Both the census and FIPS codes are assigned based on alphabetical order within Puerto Rico. Because Puerto Rico does not have incorporated places--legally defined governmental units that perform services, raise taxes, and have elected officials specifically for closely settled communities--the Census Bureau recognizes only places delineated for statistical purposes. These census designated places (CDP's) are delineated by the Puerto Rico Planning Board, following Census Bureau guidelines, for the decennial census as the statistical counterparts of incorporated places in the States. Their boundaries, which usually coincide with visible features, have no legal status. CDP boundaries may change with changes in the settlement pattern; a CDP with the same name as in previous censuses does not necessarily have the same boundaries. The Census Bureau provides data for two types of CDP's in Puerto Rico: (1) zonas urbanas, representing the governmental center of each municipio; there is no minimum population requirement for a zona urbana, and (2) comunidades (called "aldeas" in previous censuses), representing other settlements with a 1990 census population of at least 1,000. Comunidades qualified on the basis of the population counts prepared for the 1990 Postcensus Local Review Program. Because these counts were subject to change, a few may have final population counts lower than 1,000. POPULATION OR HOUSING UNIT DENSITY Population or housing unit density is computed by dividing the total population or housing units of a geographic unit (for example, Puerto Rico, municipio, place) by its land area measured in square kilometers or square miles. Density is expressed as both "persons (or housing units) per square kilometer" and "persons (or housing units) per square mile" of land area in 1990 census printed reports. STATE States are the primary governmental divisions of the United States. The District of Columbia is treated as a statistical equivalent of a State for census purposes. The Census Bureau treats the Outlying Areas as the statistical equivalents of States for presenting the 1990 census data. The Outlying Areas include American Samoa, Guam, the Commonwealth of the Northern Mariana Islands (Northern Mariana Islands), the Republic of Palau (Palau), Puerto Rico, and the Virgin Islands of the United States (Virgin Islands). Each State and equivalent entity is assigned a two-digit numeric Federal Information Processing Standards (FIPS) code in alphabetical order by State name, followed by the Outlying Area names. Each State and equivalent entity also is assigned a two-digit census code. The first digit of the code is the code for the respective division except for Puerto Rico, the Virgin Islands, and the Outlying Areas of the Pacific, which are assigned "0" as the first digit because they are not part of any division. Each State and equivalent area also is assigned the two-letter FIPS/United States Postal Service (USPS) code. TIGER TIGER is an acronym for the new digital (computer-readable) geographic data base that automates the mapping and related geographic activities required to support the Census Bureau's census and survey programs. The Census Bureau developed the Topologically Integrated Geographic Encoding and Referencing (TIGER) System to automate the geographic support processes needed to meet the major geographic needs of the 1990 census: producing the cartographic products to support data collection and map publication, providing the geographic structure for tabulation and publication of the collected data, assigning residential and employer addresses to their geographic location and relating those locations to the Census Bureau's geographic units, and so forth. The content of the TIGER data base is made available to the public through a variety of "TIGER Extract" files that may be obtained from the Data User Services Division, U.S. Bureau of the Census, Washington, DC 20233. UNITED STATES The United States comprises the 50 States and the District of Columbia. In addition, the Census Bureau treats the Outlying Areas (see "State") as statistical equivalents of States for the 1990 census. URBAN AND RURAL The Census Bureau defines "urban" for the 1990 census as comprising all territory, population, and housing units in urbanized areas and in places of 2,500 or more persons outside urbanized areas. More specifically, "urban" consists of territory, persons, and housing units in: 1. Places of 2,500 or more persons. 2. All other territory included in urbanized areas. Territory, population, and housing units not classified as urban constitute "rural." In the 100-percent data products, "rural" is divided into "places of less than 2,500" and "not in places." The "not in places" category comprises "rural" outside zonas urbanas and comunidades. In many data products, the term "other rural" is used; "other rural" is a residual category specific to the classification of the rural in each data product. In the sample data products, rural population and housing units are subdivided into "rural farm" and "rural nonfarm." "Rural farm" comprises all rural households and housing units on farms (places from which $1,000 or more of agricultural products were sold in 1989); "rural nonfarm" comprises the remaining rural. The urban and rural classification cuts across the other hierarchies; for example, there generally is both urban and rural territory within both metropolitan and nonmetropolitan areas. In censuses prior to 1950, "urban" comprised all territory, persons, and housing units in places of 2,500 or more persons. The definition of urban that restricted itself to places having 2,500 or more persons excluded many large, densely settled areas merely because they were not places. To improve its measure of urban territory, population, and housing units, the Census Bureau adopted the concept of the urbanized area. URBANIZED AREA The Census Bureau delineates urbanized areas (UA's) to provide a better separation of urban and rural territory, population, and housing in the vicinity of large places. A UA comprises one or more places ("central place") and the adjacent densely settled surrounding territory ("urban fringe") that together have a minimum of 50,000 persons. The urban fringe generally consists of contiguous territory having a density of at least 1,000 persons per square mile. The urban fringe also includes outlying territory of such density if it is connected to the core of the contiguous area by road and is within 1- 1/2 road miles of that core, or within 5 road miles of the core but separated by water or other undevelopable territory. Other territory with a population density of fewer than 1,000 people per square mile is included in the urban fringe if it eliminates an enclave or closes an indentation in the boundary of the urbanized area. The population density is determined by (1) outside of a place, one or more contiguous census blocks with a population density of at least 1,000 persons per square mile or (2) inclusion of a place containing census blocks that have at least 50 percent of the population of the place and a density of at least 1,000 persons per square mile. The complete criteria are available from the Chief, Geography Division, U.S. Bureau of the Census, Washington, DC 20233. Urbanized Area Central Place One or more central places function as the dominant centers of each UA. The identification of a UA central place permits the comparison of this dominant center with the remaining territory in the UA. There is no limit on the number of central places, and not all central places are necessarily included in the UA title. UA central places include: 1. Each place entirely within the UA that is a central city of a metropolitan area (MA). 2. If the UA does not contain an MA central city or is located outside of an MA, the central place(s) is determined by population size. Urbanized Area Title and Code The title of a UA identifies those places that are most important within the UA; it links the UA to the encompassing MA, where appropriate. If a single MA includes most of the UA, the title and code of the UA generally are the same as the title and code of the MA. If the UA is not mostly included in a single MA, if it does not include any place that is a central city of the encompassing MA, or if it is not located in an MA, the Census Bureau uses the population size of the included places to determine the UA title. The name of Puerto Rico is included in the title of each UA in the Commonwealth. The numeric code used to identify each UA is the same as the code for the mostly encompassing MA (including CMSA and PMSA). If MA title cities represent multiple UA's, or the UA title city does not correspond to the first name of an MA title, the Census Bureau assigns a code based on the alphabetical sequence of the UA title in relationship to the other UA and MA titles. VOTING DISTRICT (VTD) A voting district (VTD) is any of a variety of types of areas (for example, election districts, precincts, legislative districts) established by the Puerto Rico government for purposes of elections. For census purposes, the Puerto Rico Planning Board outlined the boundaries of VTD's around groups of whole census blocks on census maps. The entities identified as VTD's are not necessarily those legally or currently established. Also, to meet the "whole block" criterion, it may have been necessary to adjust VTD boundaries to nearby block boundaries. Therefore, the VTD's shown on the 1990 census tapes, listings, and maps may not represent the actual VTD's in effect at the time of the census. Each VTD is assigned a four-character alphanumeric code that is unique within each municipio. The code "ZZZZ" is assigned to nonparticipating areas; the Census Bureau reports data for areas coded "ZZZZ." On computer--readable files, area measurements are shown to six decimal places; the decimal point is implied.