{"id":432,"date":"2014-01-24T20:56:52","date_gmt":"2014-01-24T20:56:52","guid":{"rendered":"http:\/\/opentextbc.ca\/natureofgeographicinformation\/?post_type=chapter&p=432"},"modified":"2015-05-27T15:44:37","modified_gmt":"2015-05-27T15:44:37","slug":"1-overview-5","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/natureofgeographicinformation\/chapter\/1-overview-5\/","title":{"raw":"National Spatial Data Infrastructure I","rendered":"National Spatial Data Infrastructure I"},"content":{"raw":"

6.1. Overview<\/h2>\r\nChapters 6 and 7 consider the origins and characteristics of the framework data themes<\/strong> that make up the United States' proposed National Spatial Data Infrastructure (NSDI). The seven themes include geodetic control, orthoimagery, elevation, transportation, hydrography, government units (administrative boundaries), and cadastral (property boundaries). Most framework data, like the printed topographic maps that preceded them, are derived directly or indirectly from aerial imagery<\/strong>. Chapter 6 introduces the field of photogrammetry, which is concerned with the production of geographic data from aerial imagery. The chapter begins by considering the nature and status of the U.S. NSDI in comparison with other national mapping programs. It considers the origins and characteristics of the geodetic control and orthoimagery themes. The remaining five themes are the subject of Chapter 7.\r\n

Objectives<\/h3>\r\nStudents who successfully complete Chapter 6 should be able to:\r\n
    \r\n\t
  1. Explain how the distribution of authority for mapping and land title registration among various levels of government affects the availability of framework data;<\/li>\r\n\t
  2. Describe how topographic data are compiled from aerial imagery;<\/li>\r\n\t
  3. Explain the difference between a vertical aerial photograph and an orthoimage;<\/li>\r\n\t
  4. List and describe characteristics and status of the USGS National Map; and<\/li>\r\n\t
  5. Discuss the relationship between the National Map and the NSDI framework.<\/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

    6.2. Checklist<\/h2>\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 6 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 6<\/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\u00a0two practice quizzes<\/strong>\u00a0including:\r\n
      \r\n\t
    • National Spatial Data Legacies<\/li>\r\n\t
    • Photogrammetry<\/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 6 folder > [quiz]<\/td>\r\n<\/tr>\r\n
    3<\/th>\r\nPerform\u00a0\u201cTry this\u201d activities<\/strong>\u00a0including:\r\n
      \r\n\t
    • Compare data copyright policies of the U.S. and Britain<\/li>\r\n\t
    • Search for USGS topographic maps and aerial imagery<\/li>\r\n\t
    • View and explore a digitally scanned topographic map<\/li>\r\n\t
    • View and explore a digital orthophoto<\/li>\r\n\t
    • Assess the availability of digital orthophotos for your area<\/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 the\u00a0Chapter 6 Graded Quiz<\/strong><\/td>\r\nANGEL > [your course section] > Lessons tab > Chapter 6 folder > Chapter 6 Graded Quiz. See the Calendar tab in ANGEL for due dates.<\/td>\r\n<\/tr>\r\n
    5<\/th>\r\n\u00a0Read\u00a0comments 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 \r\n

    6.3. National Geographic Information Strategies<\/h2>\r\nIn 1998 Ian Masser published a comparative study of the national geographic information strategies of four developed countries: Britain (England and Wales), the Netherlands, Australia, and the U.S. Masser built upon earlier work which found that countries with relatively low levels of digital data availability and GIS diffusion also tended to be countries where there had been a fragmentation of data sources in the absence of central or local government coordination\u201d (p. ix). Comparing his four case studies in relation to the seven framework themes identified for the U.S. NSDI, Masser found considerable differences in data availability, pricing, and intellectual property protections. Differences in availability of core data, he found, are explained by the ways in which responsibilities for mapping and for land titles registration are distributed among national, state, and local governments in each country.\r\n\r\nThe following table summarizes those distributions of responsibilities.\r\n\r\n \r\n\r\n\r\n\r\n\r\n\r\n\r\n
    Distributions of Responsibilities<\/caption>\r\n
    <\/th>\r\n\u00a0Britain (England & Wales)<\/strong><\/th>\r\n\u00a0Netherlands<\/strong><\/th>\r\n\u00a0Australia<\/strong><\/th>\r\n\u00a0United States<\/strong><\/th>\r\n<\/tr>\r\n<\/thead>\r\n
    \u00a0Central government<\/strong><\/th>\r\n\u00a0Land titles registration, small- and large-scale mapping, statistical data<\/td>\r\n\u00a0Land titles registration, small- and large-scale mapping, statistical data<\/td>\r\nSome small-scale mapping, statistical data<\/td>\r\nSmall-scale mapping, statistical data<\/td>\r\n<\/tr>\r\n
    \u00a0State\/Territorial government<\/strong><\/th>\r\nNot applicable<\/td>\r\nNot applicable<\/td>\r\n\u00a0Land titles registration, small- and large-scale mapping<\/td>\r\n\u00a0Some land titles registration and small- and large-scale mapping<\/td>\r\n<\/tr>\r\n
    \u00a0Local government<\/strong><\/th>\r\nNone<\/td>\r\nlarge-scale mapping, population registers<\/td>\r\nSome large-scale mapping<\/td>\r\n\u00a0 Land titles registration, large-scale mapping<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\nDistribution of responsibilities among different levels of government (Masser, 1998).\r\n\r\nMasser\u2019s analysis helps to explain what geospatial professionals in the U.S. have known all along \u2014 that the coverage of framework data in the U.S. is incomplete or fragmented because thousands of local governments are responsible for large-scale mapping and land titles registration, and because these activities tend to be poorly coordinated<\/strong>. In contrast, core data coverage is more or less complete in Australia, the Netherlands, and Britain, where central and state governments have authority over large-scale mapping and land-titles registration.\r\n\r\nOther differences among the four countries relate to fees charged by governments to use the geographic and statistical data they produce, as well as the copyright protections they assert over the data.\u00a0U.S. federal government agencies, Masser notes, differ from their counterparts by charging no more than the cost of reproducing their data in forms suitable for delivery to customers<\/strong>. State and local government policies in the U.S. vary considerably, however. Longstanding debates persist in the U.S. about the viability and ethics of recouping costs associated with public data.\r\n\r\nThe U.S. also differs starkly from Britain and Australia in regards to copyright protection. Most data published by the U.S. Geological Survey or U.S. Census Bureau resides in the public domain and may be used without restriction. U.K. Ordnance Survey data, by contrast, is protected by Crown copyright, and is available for use by others for fees and under the terms of restrictive licensing agreements.\u00a0One consequence of the federal government\u2019s decision to release its geospatial data to the public domain, some have argued, was the early emergence of a vigorous geospatial industry in the U.S.<\/strong>\r\n

    TRY THIS!<\/strong><\/h3>\r\nTo learn more about the Crown copyright policy of the Great Britain\u2019s Ordnance Survey, search the Internet for \u201cordnance survey crown copyright.\u201d\r\n\r\nThe\u00a0USGS policy is explained here<\/a>\u00a0(or search on \u201cacknowledging usgs as information source\u201d)\r\n

    6.4. Legacy Data: USGS Topographic Maps<\/h2>\r\n
    Since the eighteenth century, the preparation of a detailed basic reference map has been recognized by the governments of most countries as fundamental for the delimitation of their territory, for underpinning their national defense and for management of their resources (Parry, 1987).<\/blockquote>\r\nSpecialists in geographic information recognize two broad functional classes of maps, reference maps and thematic maps. As you recall from Chapter 3, a thematic map is usually made with one particular purpose in mind. Often, the intent is to make a point about the spatial pattern of a single phenomenon.\u00a0Reference maps<\/strong>, on the other hand, are designed to serve many different purposes. Like a reference book, such as a dictionary, encyclopedia, or gazetteer, reference maps help people look up facts. Common uses of reference maps include locating place names and features, estimating distances, directions, and areas, and determining preferred routes from starting points to a destination. Reference maps are also used as base maps upon which additional geographic data can be compiled. Because reference maps serve various uses, they typically include a greater number and variety of symbols and names than thematic maps. The portion of the United States Geological Survey (USGS) topographic map shown below is a good example.\r\n\r\n\"Portion\r\n\r\nA typical reference map. A portion of a USGS topographic quadrangle map (USGS, 1971)\r\n\r\nThe term\u00a0topography<\/strong>\u00a0derives from the Greek\u00a0topographein,\u00a0<\/em>\u201cto describe a place.\u201d Topographic maps show, and name, many of the visible characteristics of the landscape, as well as political and administrative boundaries. Topographic map series provide base maps of uniform scale, content, and accuracy (more or less) for entire territories. Many national governments include agencies responsible for developing and maintaining topographic map series for a variety of uses, from natural resource management to national defense. Affluent countries, countries with especially valuable natural resources, and countries with large or unusually active militaries, tend to be mapped more completely than others.\r\n\r\nThe systematic mapping of the entire U.S. began in 1879, when the U.S. Geological Survey (USGS) was established. Over the next century USGS and its partners created topographic map series at several scales, including 1:250,000, 1:100,000, 1:63,360, and 1:24,000. The diagram below illustrates the relative extents of the different map series. Since much of today\u2019s digital map data was digitized from these topographic maps, one of the challenges of creating continuous digital coverage of the entire U.S. is to seam together all of these separate map sheets.\r\n\r\n\"Diagam\r\n\r\nRelative extents of the several USGS quadrangle map series. (Thompson, 1988).\r\n\r\nMap sheets in the 1:24,000-scale series are known as\u00a0quadrangles<\/strong>\u00a0or simply quads. A quadrangle is a four-sided polygon. Although each 1:24,000 quad covers 7.5 minutes longitude by 7.5 minutes latitude, their shapes and area coverage vary. The area covered by the 7.5-minute maps varies from 49 to 71 square miles (126 to 183 square kilometers), because the length of a degree of longitude varies with latitude.\r\n\r\n\"Topographer\r\n\r\nTopographer compiling topographic map using a plane table and alidade (NOAA, 2007).\r\n\r\nThrough the 1940s, topographers in the field compiled by hand the data depicted on topographic maps<\/strong>. Anson (2002) recalls being outfitted with a 14 inch x 14 inch tracing table and tripod, plus an alidade [a 12 inch telescope mounted on a brass ruler], a 13 foot folding stadia rod, a machete, and a canteen\u2026 (p. 1). Teams of topographers sketched streams, shorelines, and other water features; roads, structures, and other features of the built environment; elevation contours, and many other features. To ensure geometric accuracy, their sketches were based upon geodetic control provided by land surveyors, as well as positions and spot elevations they surveyed themselves using alidades and rods. Depending on the terrain, a single 7.5-minute quad sheet might take weeks or months to compile.\u00a0In the 1950s, however, photogrammetric methods<\/strong>involving stereoplotters that permitted topographers to make accurate stereoscopic measurements directly from overlapping pairs of aerial photographs provided a viable and more efficient alternative to field mapping. We\u2019ll consider photogrammetry in greater detail later on in this chapter.\r\n\r\nBy 1992 the series of over 53,000 separate quadrangle maps covering the lower 48 states, Hawaii, and U.S. territories at 1:24,000 scale was completed, at an estimated total cost of $2 billion. However, by the end of the century the average age of 7.5-minute quadrangles was over 20 years, and federal budget appropriations limited revisions to only 1,500 quads a year (Moore, 2000). As landscape change has exceeded revisions in many areas of the U.S., the USGS topographic map series has become legacy data outdated in terms of format as well as content.\r\n

    TRY THIS!<\/strong><\/h3>\r\nSearch the Internet on \u201cUSGS topographic maps\u201d to investigate the history and characteristics of USGS topographic maps in greater depth. View preview images, look up publication and revision dates, and order topographic maps at\u00a0 \u201cUSGS Store.\u201d\r\n

    6.5. Accuracy Standards<\/h2>\r\nErrors and uncertainty are inherent in geographic data.<\/strong>\u00a0Despite the best efforts of the USGS Mapping Division and its contractors, topographic maps include features that are out of place, features that are named or symbolized incorrectly, and features that are out of date.\r\n\r\nAs discussed in Chapter 2, the locational accuracy of spatial features encoded in USGS topographic maps and data are guaranteed to conform to National Map Accuracy Standards. The standard for topographic maps state that horizontal positions of 90 percent of the well-defined points tested will occur within 0.02 inches (map distance) of their actual positions. Similarly, the vertical positions of 90 percent of well-defined points tested are to be true to within one-half of the contour interval. Both standards, remember, are scale-dependent.\r\n\r\nObjective standards do not exist for the accuracy of attributes associated with geographic features. Attribute errors certainly do occur, however. A chronicler of the national mapping program (Thompson, 1988, p. 106) recalls a worried user who complained to USGS that \u201cMy faith in map accuracy received a jolt when I noted that on the map the borough water reservoir is shown as a sewage treatment plant.\u201d\r\n\r\nThe passage of time is perhaps the most troublesome source of errors on topographic maps. As mentioned in the previous page, the average age of USGS topographic maps is over 20 years. Geographic data quickly lose value (except for historical analyses) unless they are continually revised. The sequence of map fragments below shows how frequently revisions were required between 1949 and 1973 for the quad that covers Key Largo, Florida. Revisions are based primarily on geographic data produced by aerial photography.\u00a0<\/span>\r\n\r\nGeographic data quickly lose value if they are not kept up to date. (Thompson, 1988). Select each of the years to view the revised map. Note: You need to have the Adobe Flash player installed in order to see and interact with this illustration. You can download Flash Player free athttp:\/\/www.adobe.com\/flash<\/a>.\r\n

    TRY THIS!<\/strong><\/h3>\r\nInvestigate standards for data quality and other characteristics of\u00a0U.S. national map data here<\/a>\u00a0or by searching the Internet for \u201cusgs national map accuracy standards\u201d\r\n

    6.6. Scanned Topographic Maps<\/h2>\r\nMany digital data products have been derived from the USGS topographic map series. The simplest of such products are\u00a0Digital Raster Graphics<\/strong>(DRGs)<\/strong>. DRGs are scanned raster images of USGS 1:24,000 topographic maps. DRGs are useful as backdrops over which other digital data may be superimposed. For example, the accuracy of a vector file containing lines that represent lakes, rivers, and streams could be checked for completeness and accuracy by plotting it over a DRG.\r\n\r\n\"Digital\r\n\r\nPortion of a Digital Raster Graphic (DRG) for Bushkill, PA\r\n\r\nDRGs are created by scanning paper maps at 250 pixels per inch resolution. Since at 1:24,000 1 inch on the map represents 2,000 feet on the ground, each DRG pixel corresponds to an area about 8 feet (2.4 meters) on a side. Each pixel is associated with a single attribute: a number from 0 to 12. The numbers stand for the 13 standard DRG colors.\r\n\r\n\"Maginified\r\n\r\nMagnified portion of a Digital Raster Graphic (DRG) for Bushkill, PA\r\n\r\nLike the paper maps from which they are scanned, DRGs comply withNational Map Accuracy Standards<\/a>. A subset of the more than 50,000 DRGs that cover the lower 48 states have been sampled and tested for completeness and positional accuracy.\r\n\r\nDRGs conform to the Universal Transverse Mercator projection used in the local UTM zone. The scanned images are transformed to the UTM projection by matching the positions of 16 control points. Like topographic quadrangle maps, all DRGs within one UTM zone can be fit together to form a mosaic after the map \u201ccollars\u201d are removed.\r\n\r\nTo investigate DRGs in greater depth<\/strong>, visit the\u00a0USGS Topomaps website<\/a>\u00a0or search the Internet on \u201cUSGS Digital Raster Graphics\u201d\r\n

    TRY THIS!<\/strong><\/h3>\r\n

    EXPLORE A DRG WITH GLOBAL MAPPER (DLGV32 PRO)<\/h3>\r\nYou can use a free software application called\u00a0Global Mapper\u00a0<\/strong>(also known as\u00a0dlgv32 Pro<\/strong>) to investigate the characteristics of a USGS Digital Raster Graphic. Originally developed by the staff of the USGS Mapping Division at Rolla, Missouri as a data viewer for USGS data, Global Mapper has since been commercialized, but is available in a free trial version. The instructions below will guide you through the process of installing the software and opening the DRG data. Penn State students will later be asked questions that will require you to explore the data for answers.\r\nNote: Global Mapper is a Windows application and will not run under the Macintosh operating system. The questions asked of Penn State students that involve the use of Global Mapper are not graded.\r\n

    GLOBAL MAPPER (DLGV32 PRO) INSTALLATION INSTRUCTIONS<\/h4>\r\nSkip this step if you already downloaded and installed Global Mapper or dlgv32 Pro.\r\n
      \r\n\t
    1. Navigate to\u00a0globalmapper.com<\/a>\u00a0or search the Internet for \u201cGlobal Mapper\u201d or \u201cdlgv32 Pro\u201d<\/li>\r\n\t
    2. Download the trial version of the software.<\/li>\r\n\t
    3. Double-click on the setup file you downloaded to install the program.<\/li>\r\n\t
    4. Launch Global Mapper or dlgv32 Pro.<\/li>\r\n<\/ol>\r\n

      DOWNLOADING AND EXPLORING DRG DATA IN GLOBAL MAPPER<\/h4>\r\n
        \r\n\t
      1. First, create a directory called \u201cUSGS Data\u201d on your hard disk, where you can file your course materials if you haven\u2019t done so already.<\/li>\r\n\t
      2. Download the DRG.zip data archive<\/a>. The ZIP archive is 2.7 Mb in size and will take approximately 35 seconds to download via high speed DSL or cable, or about 9 minutes and 35 seconds minutes via 56 Kbps modem. Registered Penn State students who cannot download the file should contact their assigned teaching assistant for help.<\/li>\r\n\t
      3. Now decompress the archive into a directory on your hard disk.\r\n