National topographic/base data • Most countries have federal agencies charged with mapping national resources & infrastructure… • e.g., United States Geological Survey – established 1879 • many European countries far earlier • also previously created by colonial powers for colonies • these topographic “base” maps valuable spatial data source • finding and getting access can be difficult • contact the national agencies good list: http://maplib.clarku.edu/offices/maplibrary/links.htm • resellers, e.g. Omni Resources (nearby, in Burlington, NC) – www.omnimap.com
National topographic/base data • “Topographic map” • name refers to information (contour lines) about terrain/elevation = topography • “topographic maps” generally contain much more than just elevation info • Topographic base map info increasingly digital • many developed countries are well into the conversion process • U.S. nearly complete • less-developed countries much less so • even with digital source data… still need to be able to gain access, import data format, etc…
National Spatial Data Infrastructure (NSDI) • Coordinated by Federal Geographic Data Committee • FGDC formalized in 1994 -- oversee production of 100’s of federal spatial data products • 17 federal agencies + state, county, local, & tribal governments • Create standards for content & format of digital spatial data • SpatialDataTransferStandard (SDTS) • catalog of possible spatial features, defines spatial terms • profiles: topological vector profile, raster profile, point profile • metadata • Content-specific standards, e.g. • cadastral (property mapping) • wetlands & deep-water habitats • vegetation classification • soils mapping • digital orthoimagery • -- still very much a work in progress… will it be comprehensively adopted??? • FGDC also required to provide data clearinghouse • http://www.fgdc.gov/clearinghouse • Good spot to find US geographic data
USGS topographic maps • Complete coverage of the U.S. (not at all scales) • Large-scale - 1:24,000 • occasional maps at 1:25,000 (metric) • “7.5-minute quadrangle” map sheets -- 54,000 to cover contiguous U.S. and Hawaii • Alaska only available as 1:63,360 • maps include… • roads, railroads, hydrography, cemeteries, churches, schools, etc… • plus contour lines • Also 1:100,000 and 1:250,000 topographic map series • but smaller the scale less detail • Digital versions of USGS topographic maps • 1:24,000 (large scale) + 1:63,360 for Alaska • 1:100,000 (intermediate scale) • 1:2,000,000 (small scale)
USGS Data – Digital Raster Graphics (DRG) • Raster images of standard topograhpic maps • Scanned and georeferenced • include map collar • Pixel attributes…? • color value • data?
USGS – Digital Line Graphs (DLG) • 1:24:000 scale reproduces 7.5-min quads: • Boundaries (state, county, city, national parks/preserves) • Hydrography • Transportation (roads, streets, railroads) • Transmission (pipelines and powerlines) • Elevation contours and spot elevation values • Basic surface cover -- e.g., vegetation type, rock, urban, etc... • Human-made & cultural features • Geodetic survey control points & markers • 1:100,000 & 1:2,000,000 • fewer feature types included Image of USGS 1:24,000 West Rapid City (South Dakota) DLG quadrangle. Hydrography shown in cyan, roads in red, pipelines/transmission lines in green, & railroads in blue. (GIF image from USGS.)
USGS – Digital Elevation Models (DEM) • Raster-format elevation data • Elevation samples at regularly-spaced intervals • Large scale: 1:24,000 • 7.5x7.5-minute units • spatial resolution = 30x30meters • Intermediate scale: 1:100,000 • 30x30-minute units • Small scale: 1:250,000 • 1x1-degree units
Spatial data on the web… • FGDC required to provide data clearinghouse • http://www.fgdc.gov/clearinghouse • Good spot to find US geographic data • Other online data resources • www.gisdatadepot.com • http://www.esri.com/data/online • Meta-lists, e.g. Digital Elevation Data Catalog www.geo.ed.ac.uk/home/ded.html • State clearinghouses • e.g. Pennsylvania Spatial Data Access www.pasda.psu.edu/access/index.shtml • e.g. North Carolina Center for Geographic Information and Analysis www.cgia.state.nc.us • cost-recovery… • Multinational efforts… • Global Spatial Data Initiative www.gsdi.org
Data Sources U.S. Census Data & TIGER/Line Files • Census Bureau: • Charged with the Constitutional responsibility of carrying out the decennial census • Census of Population and Housing • Very large mapping component involved in undertaking a U.S. national census!
U.S. Census Data The U.S. Census acquires data from households about: • Demographic info • Race • Population • Disabilities • Migration • Economic info • Living quarters • Occupation • Income • Social info • Languages spoken • School enrollment • Family structure in the home • Marital status • Ancestry • Foreign-born population
U.S. Census Data & TIGER/Line Files • Census data collected by household • Geographic location of the household must be known • To find household to deliver questionnaire • To relate the questionnaire to a place
U.S. Census Data & TIGER/Line Files • TIGER/Line files: • The “geography” of the census • Topologically Integrated Geographic Encoding & Referencing • Examples of layers of this massive dataset: • streets • Address ranges of households • landmarks for census-taking • County/city/block boundaries
U.S. Census Data & TIGER/Line Files TIGER designed to: • support pre-census functions in preparation for Census of Population and Housing • support census-taking efforts • evaluate success of the Census • provide geographic framework for analysis of Census data
Before TIGER/Line • TIGER/Line files used in the 1990 and 2000 census • Will be used in the future by the Census Bureau • Before TIGER/Line files was GBF/DIME system • GBF/DIME • Created in 1967 • Used for the 1970 and 1980 censuses
Enumeration units for TIGER/LINE Files • Privacy issue • Data not available to public by HH • Data aggregated to larger geographic units • Prevents breaches of privacy • Allows for useful geographic data summaries
Hierarchical Organization • Subdivisional • Portrays the internal divisions of a hierarchy • Example: Regions of North Carolina
Census geographic hierarchy • hierarchical tabulation systems, e.g.: USA Region Division State County Tract Block Group Block • 2000 Census tallies for entire US: 65,443 tracts 208,790 block groups 8,205,582 blocks • for NC: 1,563 tracts 5,271 block groups 232,403 blocks
TIGER/LINE Files • Supporting geography • roads/streets/highways • basic hydrography • point & area landmarks • etc...
TIGER area (polygon) & landmark data • Point and polygon landmarks • Census geography (tracts, blocks, etc.) used for reporting Census data • ID linkage from polygons in TIGER/Line data to Census attribute data
TIGER line and address data • Roads • attributes include basic road type, address ranges
TIGER address data • address ranges: street address numbers at beginning and ending of arc/line in database • allows address geocoding match data with address to a spatial location using an interpolated estimate • data use implication: • explosion of analysis and data integration capabilities • extremely large (and growing) amount of data tied to addresses • problem: still some incomplete address range data, esp. in rural areas
Link to Census data • Census attribute data • - Summary data files • Link to Census geographic entities in TIGER/Line files using unique Census geography IDs • Lets us merge a tremendously rich source of detailed socioeconomic data (Census) with a comprehensive geography for the entire country… Orange County, NC block groups w/ median income data (darker green = higher income)
Errror/accuracy problems… • Spatial error from a variety of sources • Lines digitized from 1:100,000 scale maps • errors in source DIME files • updates from many agencies and localities across the U.S. • little or no quality control! • and more… • Official statement: meets National Map Accuracy Standards for 100,000-scale data = +/- 167 feet • But… is a high-level of spatial accuracy in TIGER necessary for Census purposes? • Another problem: • new development after updating can never keep up…
Cost of Census 2000 Products • Internet Free • CD-ROMs $50 • DVDs $60 TIGER/Line files and all kinds of Census data products at http://www.census.gov/