GIS Data Sources
Dept. of Geography Computing Orientation Fall 1999
National topographic/base data
Most countries have federal agencies charged with mapping
national resources & infrastructure…
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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
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resellers, e.g. Omni Resources (nearby, in Burlington, NC) –
www.omnimap.com
U.S. Census Data & TIGER/Line Files
National topographic/base data
“Topographic map”
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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
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many developed countries are well into the conversion process
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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…
U.S. Census Data & TIGER/Line Files
National Spatial Data Infrastructure (NSDI)
Coordinated by Federal Geographic Data Committee
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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
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Spatial Data Transfer Standard (SDTS)
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catalog of possible spatial features, defines spatial terms
profiles: topological vector profile, raster profile, point profile
metadata
Content-specific standards, e.g.
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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
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http://www.fgdc.gov/clearinghouse
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Good spot to find US geographic data
U.S. Census Data & TIGER/Line Files
USGS topographic maps
Complete coverage of the U.S. (not at all scales)
Large-scale - 1:24,000
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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…
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roads, railroads, hydrography, cemeteries, churches, schools, etc…
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plus contour lines
Also 1:100,000 and 1:250,000 topographic map series
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but smaller the scale  less detail
Digital versions of USGS topographic maps
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1:24,000 (large scale) + 1:63,360 for Alaska
1:100,000 (intermediate scale)
1:2,000,000 (small scale)
U.S. Census Data & TIGER/Line Files
USGS Data – Digital
Raster Graphics (DRG)
Raster images of standard
topograhpic maps
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Scanned and georeferenced
include map collar
Pixel attributes…?
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color value
 data?
U.S. Census Data & TIGER/Line Files
USGS – Digital Line
Graphs (DLG)
1:24:000 scale reproduces 7.5-min quads:
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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
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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.)
U.S. Census Data & TIGER/Line Files
USGS – Digital
Elevation Models (DEM)
Raster-format elevation data
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Elevation samples at regularlyspaced intervals
Large scale: 1:24,000
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7.5x7.5-minute units
spatial resolution = 30x30meters
Intermediate scale: 1:100,000
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30x30-minute units
Small scale: 1:250,000
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1x1-degree units
U.S. Census Data & TIGER/Line Files
Spatial data on the web…
FGDC required to provide data clearinghouse
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http://www.fgdc.gov/clearinghouse
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Good spot to find US geographic data
Other online data resources
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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
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e.g. Pennsylvania Spatial Data Access
www.pasda.psu.edu/access/index.shtml
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e.g. North Carolina Center for Geographic Information and Analysis
www.cgia.state.nc.us
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cost-recovery…
Multinational efforts…
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Global Spatial Data Initiative
www.gsdi.org
U.S. Census Data & TIGER/Line Files
Data Sources
U.S. Census Data & TIGER/Line Files
Census Bureau:
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Charged with the Constitutional responsibility of carrying out the
decennial census
o Census of Population and Housing
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Very large mapping component involved in undertaking a U.S.
national census!
U.S. Census Data & TIGER/Line Files
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
U.S. Census Data & TIGER/Line Files
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Census data collected by household
Geographic location of the household must be
known
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To find household to deliver questionnaire
To relate the questionnaire to a place
U.S. Census Data & TIGER/Line Files
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
U.S. Census Data & TIGER/Line Files
TIGER designed to:
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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
U.S. Census Data & TIGER/Line Files
Before TIGER/Line
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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
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Created in 1967
Used for the 1970 and 1980 censuses
U.S. Census Data & TIGER/Line Files
Enumeration units for TIGER/LINE Files
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Privacy issue
Data not available to public by HH
Data aggregated to larger geographic units
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Prevents breaches of privacy
Allows for useful geographic data summaries
U.S. Census Data & TIGER/Line Files
Hierarchical Organization
Subdivisional
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Portrays the internal divisions of a hierarchy
Example: Regions of North Carolina
Western
Mountains
U.S. Census Data & TIGER/Line Files
Piedmont
Coastal Plain
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
U.S. Census Data & TIGER/Line Files
TIGER/LINE Files
Supporting geography
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roads/streets/highways
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basic hydrography
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point & area landmarks
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etc...
U.S. Census Data & TIGER/Line Files
TIGER area (polygon) & landmark data
Point and polygon landmarks
Census geography (tracts, blocks, etc.)
used for reporting Census data
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ID linkage from polygons in
TIGER/Line data to Census
attribute data
U.S. Census Data & TIGER/Line Files
TIGER line and address data
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U.S. Census Data & TIGER/Line Files
Roads
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attributes include
basic road type,
address ranges
TIGER address data
address ranges: street address numbers at beginning and ending of
arc/line in database
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allows address geocoding
 match data with address to a spatial location using an
interpolated estimate
data use implication:
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explosion of analysis and data integration capabilities
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extremely large (and growing) amount of data tied to addresses
problem: still some incomplete address range data, esp. in rural areas
U.S. Census Data & TIGER/Line Files
Link to Census data
Census attribute data
- Summary data files
Link to Census geographic entities in
TIGER/Line files using unique
Census geography IDs
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Lets us merge a
tremendously rich source
of detailed socioeconomic
data (Census) with a
comprehensive
geography for the entire
country…
U.S. Census Data & TIGER/Line Files
Orange County, NC block groups w/
median income data (darker green =
higher income)
Errror/accuracy problems…
Spatial error from a variety of
sources
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Lines digitized from 1:100,000
scale maps
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errors in source DIME files
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updates from many agencies
and localities across the U.S.
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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:
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new development after updating
 can never keep up…
U.S. Census Data & TIGER/Line Files
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/
U.S. Census Data & TIGER/Line Files
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U.S. Census Data & TIGER/Line Files