Census geography
Census geography is the set of districts that a census-collecting agency (such as the U.S. Census Bureau) uses to aggregate data for public dissemination, since the raw individual data it collects are typically protected by privacy laws. Census geography typically includes several hierarchical levels, including governmental jurisdictions (e.g., states, provinces, counties, cities) and custom districts that the agency creates (e.g., block groups, tracts, metropolitan areas).
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U.S. Census Bureau
The focal point of the United States Census Bureau is geography. Their main goals are to "providing the framework for survey design, sample selection, data collection, tabulation, and dissemination." [1] Since the 1800s, the Census Bureau has played an important role in the creation and production of American cartography. In 1854 the Census Bureau published James D.B. DeBow's map along side census results however it was not until the early 20th/late 19th century that maps were produced regularly by the Census Bureau. In the mid-20th century the computer revolution made it possible and economical to develop and publish maps and there was a renewed interest in the development and publication of maps.[2]
Levels of Census Geography
- Census Blocks: Statistical areas bounded by visible features (roads, streams) and non-visible features such as property lines and city limits. They are the smallest geographic area that the Census Bureau uses to organize data.[3]
- Census Tracts: Small, relatively permanent statistical subdivisions of a county or equivalent entity that are updated by local participants prior to each decennial census as part of the Census Bureau's Participant Statistical Areas Program.
- Tribal Census Tracts in American Indian Areas: Consist of standard county-based census tracts tabulated within American Indian areas, thus allowing for the tracts to ignore state and county boundaries for tabulation. First introduced in the Census in 2000.[4]
How the data is collected
The several different types of data collected are as follows:
- Decennial Census of Population and Housing (collected every 10 years)
- Economic Census (collected every 5 years)
- American Community Survey (Collected variously)
The data provided by the census is helpful to show maps to the public. These maps are often displayed as choropleth maps represented at the county or state levels. Data can be represented on with nominal, ordinal, or ratio data.
Census Codes
The Census Bureau uses a variety of geographic codes to describe and differentiate between different geographic landscapes and features.
- ANSI/FIPS Codes: The American National Standards Institute (ANSI) codes are standardized numeric or alphabetic codes issued by the American National Standards Institute (ANSI) to ensure uniform identification of geographic entities through all federal government agencies.
- Class Codes: Describe the general characteristics of a geographic area related to its legal or statistical status, governmental status, and in some cases relationship to other geographic entities.[5]
- Census Tract Code and Numbers: Census tracts are identified by an up to four-digit integer number and may have an optional two-digit suffix. The suffixes are useful in helping to identify census tract changes for comparison purposes.[6]
- Functional Status Codes: Describe whether a geographic entity is a functioning governmental unit, has an inactive government, is an administrative area without a functioning government, or is a statistical area identified and defined solely for tabulation and presentation of statistical data.
- Legal/Statistical Area Description (LSAD) Codes: Describe the particular typology for each geographic entity; that is, whether the entity is a borough, city, county, town, or township, among others.
- MAF/TIGER Feature Class Codes(MTFCCs): 5-digit codes assigned by the Census Bureau intended to classify and describe geographic objects or features.
- Route Type Codes: Describes the type of road. [7]
