CS 128/ES 228 - Lecture 9a 1

Vector* Data Sources

* mostly

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[Georgian’s] First Law of GIS

Try to use somebody else’s data before you even think of

generating your own

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Geographic data portals

“Be aware” of their existence, but don’t memorize details!

Bear in mind while working on your course project

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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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Academic sites

Prominent GIS programs:

Cornell U.

U. Buffalo

U. Calif., SantaBarbara

U. Minnesota

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Commercial sites (i.e. $$)

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ESRI’s site

nice move, licensing GIS.com!)

The GIS portal!~ 100 GIS links

GIS World

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1. 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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Commercial sources of DRGsVarious companies(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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2. Digital line graphs (DLGs)

Scales 1:24,000 1:100,000 1:2 million

Full topological data structure (nodes, lines, areas + adjacency information)

Layers: 9 feature classes, street & address information, elevations

Projection: UTM (large & medium scale), Albers Conical Equal Area (small scale)

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Olean DLG: roads (4 layers)

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Olean DLG: add water features

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Olean DLG: add contours

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Olean DLG: all layers

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How are geographical features represented?

Two Mile Creek near campus

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Larger rivers: both banks (lines)

Allegheny River near campus

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Major attribute codes

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Minor attribute codes

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3. TIGER maps

U. S. Census Bureau’s DLGformat

Include county,census tract, &census block

De facto standard/source for most commercial geocoding and trip planning software

Topologically Integrated Geographic Encoding & Referencing system

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The TIGER map browser

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Center on a familiar point…

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TIGER for Allegany NY

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Census Bureau databases

American Factfinder

Reports in table or map form

Joins or relates?

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Thematic maps

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Resolution to the census tract

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Local demographic stats

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Summary: digital data sources Digital

raster graphs(DRGs)

Digital line graphs(DLGs)

TIGER files