II. THE TIGER SYSTEM: AN OVERVIEW The U.S. Bureau of the Census, in cooperation with the U.S. Geological Survey (USGS), developed a major new computer-readable geographic data base for the United States and its possessions. The primary sources of the data base were the USGS 1:100,000-scale maps and the Census Bureau's 1980 GBF/DIME-Files. The USGS compiled the 1:100,000-scale maps from photographically reduced (to 1:100,000-scale) mosaicked 1:24,000-scale maps. The USGS 1:100,000-scale maps meet national map accuracy standards and uses coordinates defined by the North American Datum, 1927 (see reference McKenzie and LaMacchia, 1987). For the lower 48 States, the cartographic quality of most of the 1990 Census TIGER/Line files, in areas outside the 1980 census GBF/DIME-File coverage and selected other large metropolitan areas, compares favorably with the USGS 1:100,000-scale maps. These geographic/cartographic files are excellent as a base for a geographic information system (GIS) but are not recommended for detailed applications requiring higher positional accuracy. The Census Bureau's TIGER System (which uses this new data base) automates the mapping and related geographic activities required to support the census and sample survey programs of the Census Bureau, starting with the 1990 Decennial Census. The TIGER System provides support for the following: - Creation and maintenance of a digital geographic data base that includes complete coverage of the United States, Puerto Rico, the Virgin Islands of the United States, American Samoa, Guam, the Northern Mariana Islands, Palau, the other Pacific entities that were part of the Trust Territories of the Pacific areas (Marshall Islands and the Federated States of Micronesia), and the Midway Islands (to provide complete mapping within the boundaries of the State of Hawaii). - Production of maps from the TIGER data base for all Census Bureau enumeration and publication programs. - Ability to assign individual addresses to geographic area codes and to the polygons (census blocks) formed by features such as roads, streams, and so forth. The design of the TIGER data base adapts the theories of topology, graph theory, and associated fields of mathematics to provide a disciplined, mathematical description for the geographic structure of the United States. The TIGER data base, at the core of the TIGER System, relates the automated description of the earth's surface with the boundary features that the Census Bureau uses in preparing its data tabulations. The topological structure of the TIGER data base defines the location and relationship of streets, rivers, and railroads to each other and to the numerous geographic areas for which the Census Bureau tabulates data from its censuses and sample surveys. It is designed to assure no duplication of these features or areas. The building of the TIGER data base involved adapting a variety of encoding techniques such as automated map scanning, manual map "digitizing," standard data keying, and sophisticated computer file matching. The goal is to provide automated access to and retrieval of the decennial census-relevant geographic information about the United States and its possessions. The geographic coverage for a 1990 Census TIGER/Line file is a county or statistically equivalent entity (see Appendix A). The files contain January 1, 1990 geographic area codes for legal boundaries obtained in response to the Census Bureau's Boundary and Annexation Survey (BAS). The 1990 Census TIGER/Line files contain the final 1990 census tabulation geographic area boundaries and codes.