{"id":274,"date":"2014-01-24T19:47:37","date_gmt":"2014-01-24T19:47:37","guid":{"rendered":"http:\/\/opentextbc.ca\/natureofgeographicinformation\/?post_type=chapter&p=274"},"modified":"2015-05-27T15:43:48","modified_gmt":"2015-05-27T15:43:48","slug":"1-overview-3","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/natureofgeographicinformation\/chapter\/1-overview-3\/","title":{"raw":"TIGER, Topology and Geocoding","rendered":"TIGER, Topology and Geocoding"},"content":{"raw":"

4.1. Overview<\/h2>\r\nIn the 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.\r\n\r\nIn 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<\/strong> 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<\/strong>.\r\n\r\nThe 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<\/strong>.\r\n\r\nMAF\/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<\/strong>.\r\n\r\nCharacteristics 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.\r\n

Objectives<\/h3>\r\nThe 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:\r\n
    \r\n\t
  1. Explain how geographic entities are represented within MAF\/TIGER;<\/li>\r\n\t
  2. Explain how geometric primitives in MAF\/TIGER are represented in TIGER\/Line Shapefile extracts;<\/li>\r\n\t
  3. Define topology and explain why and how it is encoded in TIGER;<\/li>\r\n\t
  4. Perform address geocoding; and<\/li>\r\n\t
  5. Describe how TIGER\/Line files and similar products can be used for other applications, including routing and allocation.<\/li>\r\n<\/ol>\r\n

    Comments and Questions<\/h3>\r\nRegistered students are welcome to post comments, questions, and replies to questions about the text. Particularly welcome are anecdotes that relate the chapter text to your personal or professional experience. In addition, there are discussion forums available in the ANGEL course management system for comments and questions about topics that you may not wish to share with the whole world.\r\n\r\nTo post a comment, scroll down to the text box under \"Post new comment\" and begin typing in the text box, or you can choose to reply to an existing thread. When you are finished typing, click on either the \"Preview\" or \"Save\" button (Save will actually submit your comment). Once your comment is posted, you will be able to edit or delete it as needed. In addition, you will be able to reply to other posts at any time.\r\n\r\nNote: the first few words of each comment become its \"title\" in the thread.\r\n

    Concept Map<\/strong><\/h3>\r\nYou may be interested in seeing the concept map<\/a> used to guide development of Chapters 3 and 4.\r\n

    4.2. Checklist<\/h2>\r\n \r\n\r\nThe following checklist is for Penn State students who are registered for classes in which this text, and associated quizzes and projects in the ANGEL course management system, have been assigned. You may find it useful to print this page out first so that you can follow along with the directions.\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
    Chapter 4 Checklist (for registered students only)<\/caption>\r\n
    Step<\/th>\r\nActivity<\/th>\r\nAccess\/Directions<\/th>\r\n<\/tr>\r\n<\/thead>\r\n
    1<\/th>\r\nRead<\/strong>\u00a0Chapter 4<\/td>\r\nThis is the second page of the Chapter. Click on the links at the bottom of the page to continue or to return to the previous page, or to go to the top of the chapter. You can also navigate the text via the links in the GEOG 482 menu on the left.<\/td>\r\n<\/tr>\r\n
    2<\/th>\r\nSubmit\u00a0four practice quizzes<\/strong>including:\r\n
      \r\n\t
    • MAF and TIGER<\/li>\r\n\t
    • Shapefiles<\/li>\r\n\t
    • Topology<\/li>\r\n\t
    • Geocoding<\/li>\r\n<\/ul>\r\nPractice quizzes are not graded and may be submitted more than once.<\/td>\r\n
    		Go to ANGEL > [your course section] > Lessons tab > Chapter 4 folder > [quiz]<\/td>\r\n<\/tr>\r\n
    3<\/th>\r\nPerform\u00a0\u201cTry this\u201d activities<\/strong>including:\r\n
      \r\n\t
    • Explore availability of TIGER\/Line Shapefile geographies and features<\/li>\r\n\t
    • Download and view a TIGER\/Line Shapefile<\/li>\r\n\t
    • Geocode your address using a TIGER\/Line Shapefile<\/li>\r\n\t
    • Compare the geocoding performance of online routing services<\/li>\r\n\t
    • Explore resources about the Traveling Salesman Problem<\/li>\r\n<\/ul>\r\n\u201cTry this\u201d activities are not graded.<\/td>\r\n
    		Instructions are provided for each activity.<\/td>\r\n<\/tr>\r\n
    4<\/th>\r\nSubmit theChapter 4 Graded Quiz<\/strong><\/td>\r\nANGEL > [your course section] > Lessons tab > Chapter 4 folder > Chapter 4 Graded Quiz. See the Calendar tab in ANGEL for due dates.<\/td>\r\n<\/tr>\r\n
    5<\/th>\r\n\u00a0Readcomments and questions<\/strong>posted by fellow students. Add comments and questions of your own, if any.<\/td>\r\n\u00a0Comments and questions may be posted on any page of the text, or in a Chapter-specific discussion forum in ANGEL.<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n

    4.3. MAF\/TIGER<\/h2>\r\nMAF\/TIGER is the Census Bureau\u2019s geographic database system<\/strong>. Several factors prompted the U.S. Census Bureau to create MAF\/TIGER: the need to conduct the census by mail, the need to produce wayfinding aids for census field workers, and its mission to produce map and data products for census data users.\r\n

    CONDUCTING THE CENSUS BY MAIL<\/h3>\r\nAs the population of the U.S. increased it became impractical to have census takers visit every household in person. Since 1970, the Census Bureau has mailed questionnaires to most households with instructions that completed forms should be returned by mail. Most but certainly not all of these questionnaires are dutifully mailed\u2014about 72 percent of all questionnaires in 2010. At that rate the Census Bureau estimates that some $1.6 billion was saved by reducing the need for field workers to visit non-responding households.\r\n\r\n\"Census\r\n\r\n2010 Census questionnaire.\u00a0For a question-by-question tour, go here<\/a>.\r\n\r\nTo manage its mail delivery and return operations, the Census Bureau relies upon a\u00a0Master Address File (MAF)<\/strong>. MAF is a complete inventory of housing units and many business locations in the U.S., Puerto Rico, and associated island areas. MAF was originally built from the U.S. Postal Service\u2019s Delivery Sequence File of all residential addresses. The MAF is updated through both corrections from field operations and a Local Update of Census Address (LUCA) program by which tribal, state, and local government liaisons review and suggest updates to local address records.\u00a0\u201cMAF\/TIGER\u201d refers to the coupling of the Master Address File with the TIGER spatial database<\/strong>, which together enable the Census Bureau to efficiently associate address-referenced census and survey data received by mail with geographic locations on the ground and tabulation areas of concern to Congress and many governmental agencies and businesses.\r\n\r\nIt\u2019s not as simple as it sounds. Postal addresses do not specify geographic locations precisely enough to fulfill the Census Bureau\u2019s constitutional mandate. An address is not a position in a grid coordinate system\u2013it is only one in a series of ill-defined positions along a route. The location of an address is often ambiguous because street names are not unique, numbering schemes are inconsistent, and because routes have two sides, left and right. Location matters, as you recall, because\u00a0census data must be accurately georeferenced to be useful for reapportionment, redistricting, and allocation of federal funds.<\/strong>\u00a0Thus the Census Bureau had to find a way to assign address referenced data automatically to particular census blocks, block groups, tracts, voting districts, and so on. That\u2019s what the \u201cGeographic Encoding and Referencing\u201d in the TIGER acronym refers to.\r\n

    MAPS FOR CENSUS FIELD WORKERS<\/h3>\r\nA second motivation that led to MAF\/TIGER was the need to help census takers find their way around. Millions of households fail to return questionnaires by mail, after all. Census takers (called \u201cenumerators\u201d at the Bureau) visit non-responding households in person.\u00a0Census enumerators need maps showing streets and select landmarks to help locate households.<\/strong>\u00a0Census supervisors need maps to assign census takers to particular territories. Field notes collected by field workers are an important source of updates and corrections to the MAF\/TIGER database.\r\n\r\nPrior to 1990, the Bureau relied on local sources for its maps. For example, 137 maps of different scales, quality, and age were used to cover the 30-square-mile St. Louis area during the 1960 census. The need for maps of consistent scale and quality forced the Bureau to become a map maker as well as a map user. Using the MAF\/TIGER system, Census Bureau geographers created over 17 million maps for a variety of purposes in preparation for the 2010 Census.\r\n

    DATA PRODUCTS<\/h3>\r\nThe Census Bureau\u2019s mission is not only to collect data, but also to make data products available to its constituents. In addition to the attribute data considered in Chapter 3, the Bureau disseminates a variety of geographic data products, including wall maps, atlases, and one of the earliest on-line mapping services, the TIGER Mapping Service. You can explore theBureau\u2019s maps and cartographic data products here<\/a>.\r\n\r\n\"Screenshot\r\n\r\nLaunched in 1995, the TIGER Mapping Service was one of the earliest Internet map services. Registered students will use its successor, American Factfinder, in Project 2.\r\n

    MAF\/TIGER DATABASE REDESIGN<\/h3>\r\nThe Census Bureau conducted a major redesign of the MAF\/TIGER database in the years leading up to the 2010 decennial census. What were separate, homegrown database systems (MAF and TIGER) are now unified in the industry-standard Oracle relational database management system. Benefits of this \u201ccommercial off-the-shelf\u201d (COTS) database software include concurrent multi-user access, greater user familiarity, and better integration with Web development tools. As Galdi (2005) explains in his white paper \u201cSpatial Data Storage and Topology in the Redesigned MAF\/TIGER System,\u201d the redesign \u201cmirrors a common trend in the Information Technology (IT) and Geographic Information System (GIS) industries: the integration of spatial and non-spatial data into a single enterprise data set\u201d (p. 2).\r\n\r\nConcurrent with the MAF\/TIGER redesign, the Census Bureau also updated the distribution format of its TIGER\/Line map data extracts. Consistent with the Bureau\u2019s COTS strategy, it adopted the defacto standard Esri \u201cShapefile\u201d format. The following pages consider characteristics of the spatial data stored in MAF\/TIGER and in TIGER\/Line Shapefile extracts.\r\n

    PODCAST<\/strong><\/h3>\r\nHear more about\u00a0how the Census Bureau\u2019s Geography Division uses MAF\/TIGER and related tools to create maps for the 2010 Census<\/a>.\r\n

    4.4. Vector Extracts from MAF\/TIGER<\/h2>\r\nThe Census Bureau began to develop a digital geographic database of 144 metropolitan areas in the 1960s. By 1990, the early efforts had evolved into\u00a0TIGER<\/strong>: a seamless digital geographic database that covered the whole of the United States and its territories. As discussed in the previous page, MAF\/TIGER succeeded TIGER in the lead-up to the 2010 Census.\r\n\r\nTIGER\/Line Shapefiles<\/strong>\u00a0are digital map data products extracted from the MAF\/TIGER database. They are freely available from the Census Bureau, and are suitable for use by individuals, businesses and other agencies that don\u2019t have direct access to MAF\/TIGER.\r\n\r\nThis section outlines the geographic entities represented in the MAF\/TIGER database, describes how a particular implementation of the vector data model is used to represent those entities, and considers the accuracy of digital features in relation to their counterparts on the ground. The following page considers characteristics of the \u201cShapefile\u201d data format used to distribute digital extracts from MAF\/TIGER.\r\n

    GEOGRAPHIES REPRESENTED IN TIGER AND SHAPEFILE EXTRACTS<\/h3>\r\nThe MAF\/TIGER database is selective. Only those geographic entities needed to fulfill the Census Bureau\u2019s operational mission are included. Entities that don\u2019t help the Census Bureau conduct its operations by mail, or help field workers navigate a neighborhood, are omitted. Terrain elevation data, for instance, are not included in MAF\/TIGER. A comprehensive list of the \u201cfeature classes\u201d and \u201csuperclasses\u201d included in MAF\/TIGER and Shapefiles can be found in Appendix F of theTIGER\/Line Shapefiles Technical Documentation<\/a>.\u00a0Examples of superclasses include<\/strong>:\r\n