GUS: 0262Fundamentals of GIS
Lecture Presentation 6:
Raster Data Model
Jeremy Mennis
Department of Geography and Urban Studies
Temple University
• A raster representation is composed a series of layers, each with a theme
• Typically used to represent ‘field-like’ geographic phenomena
Raster Data Model
Raster Grid
– but most common raster is composed of squares, called grid cells
– grid cells are analogous to pixels in remote sensing images and computer graphics
Raster Resolution
The distance that one side of a grid cell represents on the ground
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The higher the resolution (smaller the grid cell), the higher the precision, but the greater the cost in data storage
Raster and RDBMS
Raster layer can be attached to a RDBMS
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1 Agricultural
2 Road
3 Residential
4 Industrial
ID Land Use
Data Compression
Common Methods:
– run length encoding– value point encoding– chain codes– block codes– quadtrees
Raster Chain Codes
directions around the boundary of a region
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Start
North 1 East 1 North 2 East 2 South 3 West 3
Value 4
Raster Bock Codes
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two dimensional run length encoding