dept. of geography - computing orientation - fall 1999 gis data sources

Dept. of Geography - Computing Orientation - Fall 1999

GIS Data SourcesGIS Data Sources

U.S. Census Data & TIGER/Line Files

National topographic/base data 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 dataNational 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)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• Spatial Data Transfer Standard (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 mapsUSGS 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 USGS Data – Digital Raster Graphics (DRG)Raster Graphics (DRG)

Raster images of standard topograhpic maps

• Scanned and georeferenced• include map collar

Pixel attributes…?• color value data?


USGS – Digital Line USGS – Digital Line Graphs (DLG)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 USGS – Digital Elevation Models (DEM)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…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 Analysiswww.cgia.state.nc.us

• cost-recovery…

Multinational efforts…• Global Spatial Data Initiative

www.gsdi.org


Data SourcesData Sources

Census Bureau: • Charged with the Constitutional responsibility of carrying out the

decennial census o 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


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



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



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/LineBefore 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 FilesEnumeration 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 OrganizationHierarchical Organization

Subdivisional• Portrays the internal divisions of a hierarchy• Example: Regions of North Carolina

WesternMountains

PiedmontCoastal Plain


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

Census geographic hierarchyCensus geographic hierarchy


TIGER/LINE FilesTIGER/LINE Files

Supporting geography • roads/streets/highways • basic hydrography• point & area landmarks • etc...


TIGER area (polygon) & landmark dataTIGER 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 dataTIGER line and address data

• Roads• attributes include

basic road type, address ranges


TIGER address dataTIGER 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 dataLink 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…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…


CostCost of Census 2000 Products of Census 2000 Products

InternetInternet FreeFree

CD-ROMsCD-ROMs $50$50

DVDsDVDs $60$60

TIGER/Line files and all kinds of Census data productsat http://www.census.gov/

dept. of geography - computing orientation - fall 1999 gis data sources

Documents

data format

data clearinghousehttp

digital source data

color value data

gis data sourcesu

spatial termsprofiles

european countries

maps includeroads