Topologically Integrated Geographic Encoding and Referencing

:"TIGER redirects here. For other uses see Tiger (disambiguation)."Topologically Integrated Geographic Encoding and Referencing, or TIGER, or TIGER/Line is a format used by the United States Census Bureau to describe land attributes such as roads, buildings, rivers, and lakes, as well as areas such as census tracts. TIGER was developed to support and improve the Bureau's process of taking the Decennial Census.

The TIGER files do not contain the census demographic data, but merely the map data. GIS can be used to merge census demographics or other data sources with the TIGER files to create maps and conduct analysis. TIGER data is available without cost due to the requirement for U.S. Government publications to be released into the public domain.

Development and maintenance

Prior to the 1960 census, the Census Bureau had enumerators visit each household in the United States to have them fill out a questionnaire. The Census Bureau provided enumerators with maps, showing the assigned area to canvass. In the late 1960s, the United States Census Bureau developed Dual Independent Map Encoding (DIME), a geographic information system to handle spatial data. [cite book |author=Tomlinson, Roger |chapter=Geographic Information Systems—a New Frontier |title=Introductory readings in Geographic Information Systems |editor=Peuquet, Donna J., Duane F. Marble |publisher=Taylor & Francis |year=1991] DIME was superseded in the 1980s, with development of TIGER, which addressed problems encountered during the 1980 census with maps and geographic classifications.cite book |author=Marx, Robert W. |chapter=The TIGER system: automating the geographic structure of the United States Census |title=Introductory Readings in Geographic Information Systems |editor=Peuquet, Donna J., Duane Francis Marble |publisher=CRC Press |year=1990 |id=ISBN 0850668573] TIGER first used with the 1990 census.

All aspects of TIGER, including the data model, data structure, user interface, software applications, and map creation process, were developed in-house by Census Bureau staff, along with help from the USGS. Hydrography, railroads, and other features were scanned or digitized from USGS topographic maps (1:100,000 scale), and combined with updated addressing data from DIME and topology added. [cite journal |title=TIGER products for planning |author=Klosterman, Richard E., Alan A. Lew |journal=Journal of the American Planning Association |date=1992 |volume=58 |pages=379 |doi=10.1080/01944369208975817] The process was automated with use of batch processing, though staff manually digitized from maps to make updates to the TIGER data. [cite journal |title=U.S. Census Bureau Geographic Support: a response to changing technology and improved data |author=Trainor, Timothy |journal=Cartography and Geographic Information Science |volume=30 |year=2003 |pages=217 |doi=10.1559/152304003100011054]

TIGER defines geographic areas and features using topology, to represent the relationships between such features on a map. TIGER enables geocoding of street addresses. However, typographical errors and missing directionals and feature type attributes can result in poor or incorrect matches in some areas. While the TIGER database is concerned with linear geography, it also is used in conjunction with the Census Bureau's Master Address File (MAF). The MAF and TIGER together are used to locate all data for purposes of taking the census, and also pegging statistics to place. The Census Bureau receives a delivery sequence file from the US Postal Service and it is by use of this that it locates new and problem addresses in the MAF and TIGER. The Census Bureau periodically mails maps to municipal and county governments to allow them a chance to update and correct linework that may be in error in TIGER. A few years before each national census, the Census Bureau administers a programme known as the Local Update of Censuses Addresses (LUCA) in which it allows political jurisdictions to improve its Master Address File and TIGER.

Coverage

The TIGER/Line data includes complete coverage of the United States, Puerto Rico, the U.S. Virgin Islands, American Samoa, Guam, the Commonwealth of the Northern Mariana Islands, and the Midway Islands.

TIGER includes both land attributes such as roads, buildings, rivers, and lakes, as well as areas such as counties, census tracts, and census blocks. Some of the geographic areas represented in TIGER are political areas, including counties, congressional districts, and school districts. Others are statistical areas, including Metropolitan Statistical Areas (MSA), census tracts, census block groups, census blocks, and ZIP Code Tabulation Areas (ZCTA) which attempt to approximate, but are by no means the same as, the USPS ZIP codes. ZIP codes are not truly areas, but rather a range of deliverable addresses. Some or all of a ZIP's addresses may be reassigned to another ZIP. As many as 3% of ZIP codes undergo change each quarter. Thus, ZCTAs are statistically useless over the long term.

Technical info

The latest 2007FE release of TIGER is huge. It's size is 21,5 GB (23 182 455 508 bytes) when downloaded and needs 79,6 GB (85 513 951 614 bytes) when uncompressed.

Future

TIGER data published through February 2007 (2006 Second Edition) were in a custom text-based format, while future editions will be available for download in shapefile and GML. The Census Bureau will also make the data available through WFS and WMS servers. [ [http://www.census.gov/geo/www/tiger/future/future_tl.html Future of TIGER data] , U.S. Census Bureau] The data forms a base for OpenStreetMap in the USA.

References

External links

* [http://www.census.gov/geo/www/tiger/ U.S. Census Bureau TIGER web page]
* [http://tiger.census.gov/cgi-bin/mapsurfer Tiger Map Server Browser]