CS 128/ES 228 - Lecture 6b 1

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???