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

Regular Tessellations

Squares Triangles Hexagons

Irregular Tessellations

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 Data: Encoding

Raster Data: Encoding

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

Raster Data:

ArcGIS

Raster Data:

ArcGIS

Raster in ArcGIS – Floating Point

Raster in ArcGIS - Integer

Converting Polygons from Vector to Raster

Data Compression

Common Methods:

– run length encoding– value point encoding– chain codes– block codes– quadtrees

Run Length Encoding and

Value Point Encoding

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

Quadtreea partitioning of heterogeneous space into quarter sections

Quadtrees

• node is a quadrant that is heterogeneous

• leaf is a quadrant that is homogeneous

• quadrants are assigned an ID number according to their position and level