In Chapter 3, we studied the population data produced by the U.S. Census Bureau, and some of the ways those data can be visualized with thematic maps.
In addition to producing data about the U.S. population and economy, the Census Bureau is a leading producer of digital map data. The Census Bureau's Geography Division created its "Topologically Integrated Geographic Encoding and Referencing" (TIGER) spatial database with help from the U.S. Geological Survey. In preparation for the 2010 census, the Bureau conducted a database redesign project that combined TIGER with a Master Address File (MAF) database. MAF/TIGER enables the Bureau to associate census data, which it collects by household address, with the right census areas and voting districts. This is an example of a process called address-matching or geocoding.
The MAF/TIGER database embodies the vector approach to spatial representation. It uses point, line, and polygon features to represent streets, water bodies, railroads, administrative boundaries, and select landmarks. In addition to the "absolute" locations of these features, which are encoded with latitude and longitude coordinates, MAF/TIGER encodes their "relative" locations--a property called topology.
MAF/TIGER also includes attributes of these vector features including names, administrative codes, and, for many streets, address ranges and ZIP Codes. Vector feature sets are extracted from the MAF/TIGER database to produce reference maps for census takers and thematic maps for census data users. Such extracts are called TIGER/Line Shapefiles.
Characteristics of TIGER/Line Shapefiles that make them useful to the Census Bureau also make them valuable to other government agencies and businesses. Because they are not protected by copyright, TIGER/Line data have been widely adapted for many commercial uses. TIGER has been described as "the first truly useful nationwide general-purpose spatial data set" (Cooke 1997, p. 47). Some say that it jump-started a now-thriving geospatial data industry in the U.S.
The objective of this chapter is to familiarize you with MAF/TIGER and two important concepts it exemplifies: topology and geocoding. Specifically, students who successfully complete Chapter 4 should be able to:
- explain how geographic entities are represented within MAF/TIGER;
- explain how geometric primitives in MAF/TIGER are represented in TIGER/Line Shapefile extracts;
- define topology and explain why and how it is encoded in TIGER;
- perform address geocoding; and
- describe how TIGER/Line files and similar products can be used for other applications, including routing and allocation.
"Try This!" Activities
Take a minute to complete any of the Try This activities that you encounter throughout the chapter. These are fun, thought provoking exercises to help you better understand the ideas presented in the chapter.
You may be interested in seeing the concept map used to guide development of Chapters 3 and 4. The concept map delineates the entities and relationships that make up the contents of the two chapters.