GIS Glossary      Census Glossary      Geographic Glossary      Library Glossary


This is a dictionary of some relevant GIS terms that the iMapLibraries staff selected. Please go to for reference to a full dictionary of related terms.

    Analysis is the process of identifying a question or issue to be addressed, modeling the issue, investigating model results, interpreting the results, and possibly making a recommendation.

Area (see polygon)

      A piece of information describing a map feature. Attributes of a library might include circulation, expenditures, or in-library use.

      A map containing geographic features used for locational reference. Roads, for example, are commonly found on basemaps.

      A zone of a specified distance around features. Both constant- and variable-width buffers can be generated for a set of coverage features based on each feature's attribute values. The resulting buffer zones form polygons-areas that are either inside or outside the specified buffer distance from each feature. Buffers are useful for proximity analysis (e.g., find all stream segments within 300 feet of a proposed logging area).

    Classification method
      A formula for sorting attribute values into groups so that unique symbology can be assigned to each group. This database uses natural breaks for the ranges of population characteristics.

      A logical collection of interrelated information, managed and stored as a unit, usually on some form of mass-storage system such as magnetic tape or disk. A GIS database includes data about the spatial location and shape of geographic features recorded as points, lines, areas, pixels, grid cells, or tins, as well as their attributes.

    Data set
      A named collection of logically related data items arranged in a prescribed manner.

      To correct errors within, or modify, a computer file, a geographic data set, or a tabular file containing attribute data.

      A collection of objects (persons, places, things) described by the same attributes. Entities are identified during the conceptual design phase of database and application design.

      The geographic area displayed in a view window.

    Feature data
      In a GIS, data in vector format representing geographic objects as points such as (library locations), roads or a voting district.

        The process of identifying the coordinates of a location given its address. For example, an address can be matched against a TIGER street network to determine the location of a home. Also referred to as address geocoding.

      Geographic data
        The locations and descriptions of geographic features. The composite of spatial data and descriptive data.

        Geographic information system. An organized collection of computer hardware, software, geographic data, and personnel designed to efficiently capture, store, update, manipulate, analyze, and display all forms of geographically referenced information.

        A set of geographic features of the same type, along with their attributes. A layer is stored as a unique set of files.

        The reference area on a map that lists and explains the colors, symbols, line patterns, shadings, and annotation used on the map. The legend often includes the scale, origin, orientation, and other map information.

      Line feature
        A geographic feature that can be represented by a line or set of lines. For example, rivers, roads within a pizza delivery area, and electric and telecommunication networks are all linear features. Linear features are represented by arcs or by the route-system feature class.

        An abstract representation of the physical features of a portion of the Earth's surface graphically displayed on a planar surface. Maps display signs, symbols, and spatial relationships among the features. They typically emphasize, generalize, and omit certain features from the display to meet design objectives (e.g., railroad features might be included in a transportation map but omitted from a highway map).

      Map query
        The process of selecting information from a GIS by asking spatial or logical questions of the geographic data. Spatial query is the process of selecting features based on location or spatial relationship (e.g., select all features within 300 feet of another; point at a set of features to select them). Logical query is the process of selecting features whose attributes meet specific logical criteria (e.g., select all polygons whose value for AREA is greater than 10,000 or select all streets whose name is 'Main St.'). Once selected, additional operations can be performed, such as drawing them, listing their attributes or summarizing attribute values.

        Information about the content, quality, condition and other characteristics of data.

        To move the viewing window up, down, or sideways to display areas in a geographic data set which, at the current viewing scale, lie outside the viewing window. See also zoom.

      Point feature
        A single x,y coordinate that represents a geographic feature too small to be displayed as a line or area; for example, the location of a mountain peak or a building location on a small-scale map.

        A coverage feature class used to represent areas. A polygon is defined by the arcs that make up its boundary and a point inside its boundary for identification. Polygons have attributes that describe the geographic feature they represent. Examples of polygon features include census tracts, lakes, and voting districts.

        A logical statement used to select features or records. A simple query contains a field name, an operator and a value.

      Radius(see 'buffer')

          In an attribute table, a single 'row' of thematic descriptors.

        Relational database
          A method of structuring data as collections of tables that are logically associated to each other by shared attributes. Any data element can be found in a relation by knowing the name of the table, the attribute (column) name, and the value of the primary key.

          A record in an attribute table. The horizontal dimension of a table composed of a set of columns containing one data item each.

          A graphic pattern used to represent a feature. For example, line symbols represent arc features; marker symbols, points; shades symbols, polygons; and text symbols, annotation. Many characteristics define symbols, including color, size, angle, and pattern.

          A set of data elements that has a horizontal dimension (rows) and a vertical dimension (columns) in a relational database system. A table has a specified number of columns but can have any number of rows. A table is often called a relation. Rows stored in a table are structurally equivalent to records from flat files in that they must not contain repeating fields.

        Thematic map
          A map that reveals the geographic patterns in a statistical area.

          A user-defined perspective on a coverage, grid, tin or image geographic data set specified, if applicable, by a coverage name and feature class or data set name, attributes of interest, a data classification scheme, and theme-specific symbology for drawing.

          The Topologically Integrated Geographic Encoding and Referencing data format used by the U.S. Census Bureau to support census programs and surveys. It was used for the 1990 census. TIGER files contain street address ranges along lines and census tract/block boundaries. This descriptive data can be used to associate address information and census/demographic data with coverage features.

          To enlarge and display greater detail of a portion of a geographic data set.


        For more detail please refer to the US Census Bureau's glossary of terms

        Ability to Speak English
          For a respondent who speaks a language other than English at home, refers to hi/her assessment of his ability to speak English, from "very well" to "not at all."

          Age is generally derived from date of birth information and is based on the age of the person in complete years. The question on age has been asked since the first census of the population in 1790. Age is considered the single most important Census variable. Age affects and indicates all aspects of a person's life.

          A son or daughter by birth, an adopted child or a stepchild, regardless of the child's age or marital status.

        Children under 18 years (by household)
          Children under age 18 in a household. A household includes all the people who occupy a housing unit as their usual place of residence. (see 'own children' in this glossary.)

        Contract Rent
          The monthly rent agreed to or contracted for, regardless of any furnishings, utilities, fees, meals or services that may be included. For vacant units it is the monthly rent asked for the rental unit at the time of interview.

          Earnings is defined as the algebraic sum of wage or salary income and net income from self-employment. Earnings represent the amount of income received regularly before deductions for personal income taxes, social Security, bond purchases, union dues, Medicare deductions, etc.

        Education (Educational Attainment)
          refers to the highest level of education completed in terms of the highest degree or the highest level of schooling completed.

        Female householder, no husband present
          A female maintaining a household with no husband of the householder present.

        Gender (Sex)
          An individual's gender classification - male or female.
          Most studies indicate that sex as a single variable, is not an indicator of library use. Yet sex in combination with other variables can be a strong predictor

        Gender and Age
          An individual's gender classification- male or female. The age groupings are collapsed by the GeoLib staff-these do not necessarily match the groupings offered by the US Census.

        Grade in Which Enrolled
          The level of enrollment in school, nursery school through college and graduate or professional school.

        Hispanic or Latino by Race: Universe Total Population
          A self designated classification for people who origins are from Spain, the Spanish speaking countries of Central or South America, the Caribbean, or those identifying themselves generally as Spanish, Spanish-American, etc. Origin can be viewed as ancestry, nationality, or country of birth of the person or person's parents or ancestors prior to their arrival in the United States.

          A household includes all the people who occupy a housing unit as their usual place of residence.

        Household size
          The total number of people living in a housing unit.

        Household type and relationship
          Households are classified by type according to the sex of the householder and the presence of relatives. Examples include: married-couple family; male householder, no wife present; female householder, no husband present; spouse (husband/wife); child; and other relatives.

          The person, or one of the people in whose name the home is owned, bein bought or rented.

        Housing Units
          A house, an apartment, a mobile home or trailer, a group of rooms or a single room occupied as separate living quarters or if vacant, intended for occupancy as separate living quarters. Separate living quarters are those in which the occupants live separately from any other individuals in the building and which have direct access from outside the building or through a common hall. For vacant units, the criteria of separateness and direct access are applied to the intended occupants whenever possible.

          Income is the sum of the amounts reported separately for wages, salary, commissions, bonuses or tips, etc. Median Income divides the income distribution into two equal groups, one having incomes above the median, and other having incomes below the median.

        Language Spoken at Home
          The language currently used by respondents at home, either" English only" or a non-English language which is used in addition to English or in place of English.

        Linguistic Isolation: Household Language by
          A household in which no person 14 years old and over speaks only English and no person 14 years old and over who speaks a language other than English speaks English ''Very well ''is classified as ''linguistically isolated. ''In other words, a household in which all members 14 years old and over speak a non-English language and also speak English less than ''Very well ''(have difficulty with English) is ''linguistically isolated. ''All the members of a linguistically isolated household are tabulated as linguistically isolated, including members under 14 years old who may speak only English.

        Median income (see income)

            Information about the content, quality, condition and other characteristics of data(This database has metadata associated with select map layers.)

          Occupied housing unit
            A housing unit is classified as occupied if it is the usual place of residence of the person or group of people living in it at the time of enumeration.

          Own Children (see children under 18)
            A child under 18 years old who is a son or daughter by birth, marriage (a stepchild) or adoption.

          Owner Occupied Housing
            A housing unit is owner occupied if the owner or co-owner lives in the unit even if it is mortgaged or not fully paid for.

          Per capita income
            Average obtained by dividing aggregated income by total population of an area.

            A concentration of population either legally bounded as an incorporated place, or identified as a Census Designated Place (CDP) including comunidades and zonas urbanas in Puerto Rico. Incorporated places have legal descriptions of borough (except in Alaska and NY), city, town (except in New England, NY, and Wisconsin), or village.

            All people, male and female, child and adult, living in a given geographic area.

            The US Census Bureau uses a set of money income thresholds that vary by family size and composition to detect who is poor. If the total income for a family or unrelated individual falls below the relevant poverty threshold, then the family or unrelated individual is classified as being " below the poverty level."

            Race is a self identification data item in which respondents choose the race or races with which they most closely identify.

          Race/Ethnic origin
            Six categories make up the population reporting only one race: White, Black or African American, American Indian and Alaska Native, Asian, Native Hawaiian and Other Pacific Islander, or some other race (Hispanic is not considered a race but is available to check in the category following race.)

          Renter-occupied housing unit
            All occupied units which are not owner occupied, whether they are rented for cash rent or occupied without payment of cash rent, are classified as renter-occupied.

          Residence 5 years ago
            Indicates the area of residence 5 years prior to the reference date for those who reported that they lived in a different housing unit.

          Sex (see 'gender')

              A self-designated classification for people whose origins are from spain, the Spanish-speaking countries of Central or south America, the Caribbean, or those identifying themselves generally as Spanish, Spanish-American, etc. Origin can be viewed as ancestry, nationality, or country of birth of the person or person's parents or ancestors prior to their arrival in the US.

            Tenure by vehicles available
              Number of vehicles at the household. Tenure refers to the distinction between owner-occupied and renter occupied housing units.

            Travel Time to Work for workers 16 Years and over
              Journey to work- includes data on where people work, how they get to work, how long it takes to get from their home to heir usual workplace, when they leave home to go to heir usual workplace and carpooling.


            Some of these terms are in the US Census glossary . Others are included for the user's convenience from various sources.

              Map content including geographic, physical, cultural, political, and statistical features for locational reference.

              A subdivision of a census tract. A block is the smallest geographic unit for which Census Bureau tabulates 100% data. Many block correspond to individual city block bounded by streets, but blocks--especially in rural areas-may include many square miles and may have some boundaries that are not streets. Over 8 million blocks are identified for Census 2000.

            Block Group(also 'census block')
              A subdivision of a census tract, a block group is the smallest geographic unit for which the Census Bureau tabulates sample data. A block group consists of all the blocks within a census tract with the same beginning number.

            Census Geography
              A collective term referring to the types of geographic areas used by the Census Bureau in its data collection and tabulation operations, including their structure, designations and relationships to one another.

            Census Tract
              A small, relatively permanent statistical subdivision of a county delineated by a local committee of census data users for the purpose of presenting data. Census tract boundaries normally follow visible features in some instances; they always nest within counties. Designed to be relatively homogeneous units with respect to population characteristics, economic status, and living conditions at the time of establishment, census tracts average about 4,000 inhabitants.

              A type of incorporated placein 49 states and the District of Columbia.

            Congressional District (CD)
              An area established by law for the election of representatives to the United States congress. Each CD is to be as equal in population to all other CDs in the state as practicable, based on the decennial census counts. The number of CDs in each state may change after each decennial census and the boundaries may be changed more than once during a decade.

            County and Equivalent Entity
              The primary legal subdivision of most states. In Louisiana, these subdivisions are known as parishes. In Alaska, which has no counties, the county equivalents are boroughs, a legal subdivision and census areas, a statistical subdivision. In four states (Maryland, Missouri, Nevada and Virginia), there are one or more cities that are independent of any county and thus constitute primary subdivisions of their states. The District of Columbia has no primary divisions and the entire area is considered equivalent to a county for statistical purposes.

              Any part of the landscape, whether natural (such as a lake or river), or artificially defined (roads, state boundaries, census tracts/blocks, etc.)

            Geographic Area
              You must have a geographic boundary identified from which to extract any census variable. These basic areas that will be available in this database are from a county, a census tract (which averages 4,000, but as high as 8,000 people), to census tract subunits, block groups (50-2000), or blocks (for population numbers only.). For a library you would want a market area to be approximate to where your customers live or travel from to the library.

            State and equivalent entity
              The primary legal subdivision of the United States. The district of Columbia, Puerto Rico and the Island Areas (the U.S. virgin Islands, Guam, American Samoa, and the Northern Mariana Islands) are each treated as the statistical equivalent of a state for census purposes.

            State legislative district (SLD)
              An area from which members are elected to state legislatures. The SLDs embody the upper (senate) and lower (house) chambers of the state legislature. (Nebraska has a unicameral legislature that is represented as an upper chamber legislative entity.)

              A minor civil division in the New England states, NY, and Wisconsin and a type of incorporated place in 30 states and the Virgin Islands of the United States.

            Tract Number
              Used to uniquely identify a census tract within a county.

            Voting District (VTD)
              Any of a variety of areas, such as election districts, precincts, legislative districts, or wards, established by states and local governments for voting purposes.


            The library use data is extracted from the Federal State Cooperative System data of the National Center for Education Statistics. Refer to 'metadata' for more information. This publication has the complete glossary of terms (pp 90-107.)

            Administrative entity
              This is the public library or cooperative service that is legally established under local or state law to provide public library service to a particular client group (for example, the population of a local jurisdiction). The Administrative entity may be administrative only and have no outlets, it may have a single outlet, or it may have more than one outlet.

              Librarians with master's degrees from programs of library and information studies accredited by the American Library Association. Note: Report figures as of the last day of the fiscal year. Include all positions funded in the library's budget whether those positions are filled or not. To ensure comparable data, 40 hours per week has been set as the measure of full-time employment (FTE).

              These are materials on which sounds (only) are stored (recorded) and that can be reproduced (played back) mechanically or electronically, or both. Included are records, audiocassettes, audio cartridges, audiodiscs, audioreels, talking books, and other sound recordings.

            Book/serial volumes
              Books are non-periodical printed publications bound in hard or soft covers, or in loose-leaf format. Serials are publications issued in successive parts, usually at regular intervals, and as a rule, intended to be continued indefinitely. Serials include periodicals (magazines), newspapers, annuals (reports, yearbooks, etc.), memoirs, proceedings, and transactions of societies. Except for the current volume, count unbound serials as a volume when the library has at least half of the issues in a publisher's volume.

              A bookmobile is a traveling branch library. It consists of at least all of the following: 1) a truck or van that carries an organized collection of library materials; 2) a paid staff; and 3) regularly scheduled hours (bookmobile stops) for being open to the public. Note: Count the number of vehicles in use, not the number of stops the vehicle makes.

            Branch library
              A branch library is an auxiliary unit of an Administrative Entity which has at least all of the following: 1) separate quarters; 2) an organized collection of library materials; 3) paid staff; and 4) regularly scheduled hours for being open to the public.

            Capital Outlay
              These funds for the acquisition of or additions to fixed assets such as building sites, new buildings and building additions, new equipment, initial book stock, furnishings for new or expanded buildings and new vehicles. This excludes replacement and repair of existing furnishings and equipment, regular purchase of library materials, and investments for capital appreciation.
              Note: Local accounting practices shall determine whether a specific item is a capital expense or an operating expense regardless of the examples in the definition.

            Central library
              This is one type of single outlet library or the library which is the operational center of a multiple-outlet library. Usually all processing is centralized here and the principal collections are housed here. Synonymous with main library.
              Note: Not all Administrative Entities have a central library and some Administrative Entities have more than one central library.

            Children's program attendance
              The count of the audience at all programs for which the primary audience is children. Includes adults who attend programs intended primarily for children.

              Note: Output Measures for Public Library Service to Children: A Manual of Standardized Procedures (ALA, 1992) defines children as persons age 14 and under.
              The total annual circulation of al library materials of all types including renewals.

            Circulation of children's materials
              The total annual circulation of all children's materials in all formats to all users. It includes renewals.

            Collection expenditures
              This includes all expenditures for materials purchased or leased for use by the public. It includes print materials, microforms, machine-readable materials, audiovisual materials, etc.

            Federal government operating income
              This includes all federal government funds distributed to public libraries for expenditure by the public libraries, including federal money distributed by the state.

            Hours open (see public service hours)

              Income (total)
                This includes income from the local government, the state government, the Federal government and all other income.

              Interlibrary loans provided to
                These are library materials, or copies of the materials, provided by one library to another upon request. The libraries involved in interlibrary loans are not under the same library administration. These data are reported as annual figures.

              Interlibrary loans received from
                These are library materials, or copies of the materials, received by one library from another library upon request. The libraries involved in interlibrary loans are not under the same library administration. These data are reported as annual figures.

                These are persons with the title of librarian who do paid work that usually requires professional training and skill in the theoretical or scientific aspects of library work, or both, as distinct from its mechanical or clerical aspect. This data element also includes ALA- MLS.

              Library visits
                This is the total number of persons entering the library for whatever purpose during the year.
                Note: If an actual count of visits is unavailable, determine an annual estimate by counting visits during a typical week in October and multiplying the count by 52. A "typical week" is a time that is neither unusually busy nor unusually slow. Avoid holiday times, vacation periods for key staff, or days when unusual events are taking place in the community or the library. Choose a week in which the library is open its regular hours. Include seven consecutive calendar days, from Sunday through Saturday (or whenever the library is usually open).

              Local government operating income
                This includes all tax and non-tax receipts designated by the community, district, or region and available for expenditure by the public library. Do not include the value of any contributed or in-kind services or the value of any gifts and donations, fines, or fees.

              Metropolitan Area, but not within central city limits
                A large population nucleus, together with adjacent communities that have a high degree of economic and social integration with that nucleus. Some Metropolitan Areas are defined around two or more nuclei. Each Metropolitan Area must contain a place with a minimum population of 50,000 or a Census Bureau defined urbanized area and a total Metropolitan Area population of at least 100,000 (75,000 in New England). A Metropolitan Area comprises one or more central counties. (Independent cities are considered county equivalents.) A Metropolitan Area may also include one or more outlying counties that have close economic and social relationships with the central county. An outlying county must have a specified level of commuting to the central counties and also must meet certain standards regarding metropolitan character, such as population density, urban population, and population growth. In New England, Metropolitan Areas are composed of cities and towns rather than whole counties.

              Operating Expenditures (total)
                Operating expenditures are from the current and recurrent costs necessary to support the provision of library services.

              Other operating expenditures
                This includes all expenditures other than those for staff and collection.

              Other paid staff
                This includes all other FTE employees paid from the reporting unit budget, including plant operations, security, and maintenance staff.
              Population of the legal service area
                The number of people in the geographic area for which a public library has been established to offer services and from which (or on behalf of which) the library derives income, plus any areas served under contract for which the library is the primary service provider.
                Note: The determination of this population figure shall be the responsibility of the state library agency.

              Public library
                A public library established under state enabling laws or regulations to serve the residents of a community, district, or region. A public library is an entity that provides at least the following: 1) an organized collection of printed or other library materials, or a combination thereof; 2) a paid staff to provide and interpret such materials as required to meet the informational, cultural, recreational, and/or educational needs of a clientele; 3) an established schedule in which services of the staff are available to clientele; and 4) the facilities necessary to support such a collection, staff, and schedule.
                Note: State law determines whether an entity is a public library.

              Public service hours/year
                This is the sum of annual public service hours for outlets.

              Reference transactions
                A reference transaction is an information contact which involves the knowledge, use, recommendations, interpretation, or instruction in the use of one or more information sources by a member of the library staff. It includes information and referral services. Information sources include printed and non-printed materials, machine-readable databases, catalogs and other holdings records, and through communication or referral, other libraries and institutions and people inside and outside the library. The request may come in person, by phone, by fax, by mail, or by electronic-mail from an adult, a young adult or a child. These counts may be estimated.

              Salaries & wages expenditures
                This includes salaries and wages for al library staff (including plant operations, security, and maintenance staff) for the fiscal year. Include salaries and wages before deductions but exclude employee benefits.

              State government income
                These are all funds distributed to public libraries by state government for expenditure by the public libraries, except for federal money distributed by the state. This includes funds from such sources as penal fines, license fees and mineral rights.

              Total circulation (see circulation)

                Total income (see income)

                  Total staff (paid employees)
                    This is the sum of total librarians and al other paid staff.

                    These are materials on which pictures are recorded, with or without sound. Electronic playback reproduces pictures, with or without sound, using a television receiver or monitor.