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CS 128/ES 228 - Lecture 7a 1
Digital Map Sources II
CS 128/ES 228 - Lecture 7a 2
The first rule of building a GIS
Try to use somebody else’s data before you even think of
generating your own
CS 128/ES 228 - Lecture 7a 3
4. Vector data formats
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Digital line graphs (DLGs) Scales 1:24,000 1:100,000 1:2x106
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)
CS 128/ES 228 - Lecture 7a 5
DLG Topology
Lines = ordered sets of points with a node at each end. They can’t cross themselves or other lines
Nodes = endpoints of lines(points are degenerate lines that start and end at the same node!)
Areas = continuous regions bounded by lines. Not true polygons – areas are constructed from bounding lines and an area identifier
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Area hybrid topology
Network & area info in same file
All closed line circuits define areas – but not all areas havecartographicidentities
Hydrology ex: lakes and streams
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Tributaries are single lines
Two Mile Creek near campus
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Rivers are made of 2 lines
Allegheny River near campus
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Major feature classes
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Major attribute codes
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Minor attribute codes
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Olean DLG: all layers
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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 railroads
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Olean DLG: add contours
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5. 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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TIGER files in ArcMap
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Census IDs
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Census Bureau databases
American Factfinder
Reports in table or map form
Joins or relates?
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NYS Income, by county
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Resolution to the census tract
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Local demographic stats
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Local housing costs
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Thematic Census maps
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Themes may be reclassified
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Equal frequency classification
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Summary: digital data sources
Digital raster graphs(DRGs)
Digital line graphs(DLGs)
TIGER files
