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Digital Map Sources I
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The first rule of building a GIS
Try to use somebody else’s data before you even think of
generating your own
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1. Geographic data portals
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Nat. Geospatial Data Clearinghouse
Composed of many federal agency reps.
Developing the National Spatial Data Infra-structure
Working with Office of Homeland Security
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USGS: National Mapping Info.
Primary responsibility for US mapping
Mapping standards and metadata
Topographic maps
GNIS
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US Bureau of the Census
Address and population data, tied to the census tract
TIGER maps
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NYS GIS Clearinghouse
Familiar site?
Statewide aerial photographs
DOT maps
Gateway to many USGS & NYS products
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University sites
Prominent GIS programs:
Cornell U.
U. Buffalo
U. Calif., SantaBarbara
U. Minnesota
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Commercial sites
ESRI’s site (nice move, licensing GIS.com!)
The GIS portal!~ 100 GIS links
GIS World
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2. Geographic exchange formats
De facto standard: a.k.a. “industry standard” based on market success of a particular software standard (ex. ArcView shapefile)
De jure standard: developed by professional organization, such as ANSI or ISO (ex. SDTS in US)
Regulatory standard: enforced by government (ex. cadastre maps for property/tax purposes)
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Value of digital exchange standards
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Examples of national standards
SDTS (US): Spatial Data Transfer Standard (now mandatory for all federal agencies)
CGIS (Canada): Canadian Geomatics Interchange Standard
NTS (UK): National Transfer Standard
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3. Raster data formats
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Remote sensing data sets
NASA’s EOS program
France’s SPOT
http://earthobservatory.nasa.gov
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EOS 19 Feb news item:
Lack of Snow Drives Iditarod
North
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Digital Raster graphs (DRGs)
Scanned topographic maps at various scales
Resolution: 400 dpi typical
Projection and coordinate system: varies (read the metadata!)
Accuracy: roughly that of paper source maps
Layers: either 1 or 2. No full GIS capability
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Sources of DRGs
Commercial sources(e.g., Delorme, Silva)
1:24,000 or 1:100,000
~ $100/state
various tools, but one layer
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3-D renderings
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USGS DRGs
1:24,000 or 1:100,000
two layers - features - topography
feature classes can’t be separated
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DRG – viewing both layers
The contour layer covers the features layer!
What to do???