GIS data sources: Digital vs' Analog

1
GIS data sources Digital vs. Analog

• GIS data must be in digital form, i.e., on
  computer files. Often must be converted into the
  correct format.
• Analog - an analog representation is where a
  feature or object is represented by another
  tangible medium e.g., maps.
• Analog data must be geocoded, put into computer
  readable form, e.g., by digitizing or scanning.

2
Digital data

• Available in from many sources
• within your agency - always look in-house first.
• other agencies, e.g., Bureau of the Census,
  Bureau of Transportation Statistics, Department
  of Natural Resources, U.S. Geological Survey
• TIGER files, national transportation database,
  etc.
• Data clearinghouses
• commercial sources, e.g., ESRI, MapInfo, ETAK,
  and many others

3
Digital Data

• Most common ways to acquire digital data are from
  the Web, FTP sites, and on CD.
• Digital data often must be converted to the
  format of the GIS software package you are using.
  
• It is important to understand the associated
  metadata (data about data) when acquiring digital
  data (or providing such data to others).

4
Digital data

• For vector data, often both geographic/ spatial
  data and attribute data can be acquired.
• Geographic/spatial - states, counties, census
  tracts, zip codes, roads, airports, etc.
• Attribute - population, social/demographic
  characteristics, economic characteristics.
• These two are then linked by a key field.

5
Types of digital data

• Socio-economic
• US Census, TIGER files, etc.
• Environmental/Natural Resource
• thematic soils, land use, vegetation
• topographic elevations, roads, railroads,
  cultural features, hydrology, public land survey
  system (township and range)
• remote sensing satellite, e.g, Landsat, data and
  air photos used to get data on land use,
  vegetation, etc.

6
Spatial Data Sources - Federal

• United States Geological Survey
• Department of Agriculture
• Department of Defense
• Department of the Interior
• National Aeronautics and Space Administration
• Department of Commerce
• Department of Transportation

7
Spatial Data Souces - State/Local

• State Departments of Natural Resources
• State Departments of Transportation
• Metropolitan/Regional Planning Organizations
• County/City Governments
• Spatial data clearinghouses

8
Attribute Data Sources -Federal

• U.S. Census Bureau
• Bureau of Economic Analysis
• Bureau of Labor Statistics
• National Center for Health Statistics
• National Center for Education Statistics
• National Center for Criminal Justice Statistics
• Bureau of Transportation Statistics
• Internal Revenue Service

9
Attribute Data Sources - State/local

• State Departments of Revenue, Employment, Natural
  Resources, Transportation, etc.
• County/City governments

10
Attribute Data Sources - Other

• Private Sector
• Types of Services
• pollsters and market surveyors
• remarketers/updaters of federal data
• data aggregators collect data from state and
  local govts
• Firms/vendors
• Claritas/National Planning Data Corporation,
  Equifax/National Decision Systems, Blackburn/
  Urban Decision Systems, SMI/Donnelly Marketing,
  Dun and Bradstreet (firms), TRW-REDI (property
  data), Reebie and Associates, REMI

11
Digital Line Graphs (DLGs)

• Developed by the United States Geological Survey
  (USGS)
• Digital representations of cartographic line
  information on USGS map series
• Scales 12M, 1100K, 124K (data availability
  varies)
• Basic attribute information included

12
Digital Line Graphs (DLGs)

• Layers include (depending on scale) hydrology,
  wetlands, contours/elevation, transportation
  (roads, rails, pipelines, etc.), political and
  administrative boundaries, public land survey
  systems (PLSS), vegetative and non-vegetative
  surfaces, survey control points, some manmade
  features

13
TIGER Files

• Topologically Integrated Geographic Encoding and
  Reference File
• Developed by U.S. Bureau of the Census for 1990
  census
• Based on DLG (rural) and DIME (urban) files
• Scale 1100K

14
TIGER Files

• Includes hydrography, roads, railroads, census
  blocks, block groups, census tracts, address
  ranges, voting districts, zip codes, incorporated
  places, landmarks, etc.
• Polygons (blocks, zip codes, counties, etc.) can
  be linked with (attribute) Census data using
  common identifiers

15
DEMs/DOQs/DRGs

• DEMs - Digital Elevation Model
• Raster elevation data
• Based on 124K USGS maps
• Elevations at 30m spacing
• DOQs - Digital Ortho Quads
• In preparation
• Digital image of an aerial photo, displacement
  from lens, airplanes position, and terrain
  removed
• Image characteristics of a photo, geometric
  properties of a map
• Scale 112k, 1 meter resolution, 33 feet (10m)
  positional accuracy

16
DEMs/DOQs/DRGs

• DRGs - Digital Raster Graphics
• Scanned images of USGS topographic maps
• Used as backdrop/validation for other digital
  data

17
Satellite data, remote sensing

• Remote sensing - the measurement or acquisition
  of information of some property of an object or
  phenomena, by a recording device that is not in
  physical or intimate contact with the object or
  phenomena being studied (Manual of Remote
  Sensing)
• Two basic types
• using cameras and film, which then may be scanned
  (mainly aerial photographs)
• using sensors which directly output digital data
  (mainly satellites, but also planes)

18
Remote Sensing

• Photographic film types
• monochrome (black and white)
• natural color
• infra-red (normally to invisible to humans, good
  for geology, vegetation, heat)

19
Remote Sensing

• Types of sensors
• passive (most common) record natural
  electromagnetic energy emissions from surface
• active (radar) record reflected value of a
  transmitted signal (e.g. Canadas RADARSAT,
  NASAs SIR-C/X-SAR)
• penetrate clouds also, some ground penetration
  possible.

20
LANDSAT

• First LANDSAT satellite launched in 1972
• Commercial spinoff EOSAT
• Orbits at 700 km
• Has multispectral Thematic Mapper (TM)
• Collects data in revolving bands around earth,
  185 km wide
• 16-day cycle
• Pixels are 30m by 30m on the ground