History

Technology

Dual Independent Map Encoding

The U.S. Census Bureau developed Dual Independent Map Encoding (DIME)
during a 1967 test of procedures for the 1970 census in New Haven, CT.

Dual Independent Map Encoding (DIME) is an encoding system developed by the U.S. Census Bureau for efficiently storing geographical data and was a key technical development on the "road" toward the geographic information systems (GIS) used today. The development of DIME was assisted by Census Bureau mathemetician James Corbett. In 1967, researchers were attempting to convert analog maps into numerically encoded renderings using data from the 1967 pretest of mailout/mailback procedures in New Haven, CT, but found the process to be bogged down by redundant operations. Corbett introduced the basic ideas of the vector paradigm to the programmers who then created a protocol called DIME.

Within DIME, intersections, streets, and blocks became analogous to points, lines, and polygons, respectively. The latter group of objects would come to represent the essence of vector data, a structure rooted in Cartesian coordinate geometry. DIME also incorporated the ability to edit topology, a term used to describe the geometric relationships between vector objects.

The file format developed for storing the DIME-encoded data was known as Geographic Base Files (GBF). GBF-DIME files were digitized for all U.S. cities in the 1970s and provided a schematic map of a city's streets, address ranges, and geostatistical codes relating to the Census Bureau's tabular statistical data.

The GBF-DIME files developed in the 1970s and 1980s later became a key component in the development of the Topologically Integrated Geographic Encoding and Referencing (TIGER) system created for the 1990 census.

For more information on the development of DIME, see the September 6, 1968 , Census Bulletin article, "Dime Underwent Lots of Testing Too."