1 / 25

GIS Data Sources

GIS Data Sources. 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

toan
Download Presentation

GIS Data Sources

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. GIS Data Sources

  2. 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

  3. 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…

  4. 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

  5. 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)

  6. USGS Data – Digital Raster Graphics (DRG) • Raster images of standard topograhpic maps • Scanned and georeferenced • include map collar • Pixel attributes…? • color value •  data?

  7. 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.)

  8. 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

  9. 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

  10. 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!

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. Hierarchical Organization • Subdivisional • Portrays the internal divisions of a hierarchy • Example: Regions of North Carolina

  18. 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

  19. TIGER/LINE Files • Supporting geography • roads/streets/highways • basic hydrography • point & area landmarks • etc...

  20. 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

  21. TIGER line and address data • Roads • attributes include basic road type, address ranges

  22. 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

  23. 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)

  24. 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…

  25. 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/

More Related