GUS: 0265Fundamentals of GIS

Lecture Presentation 4:

Raster Data Model and Operations

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 Resolution

The distance that one side of a grid cell represents on the ground

1

22

4

4

1

1

4

4

1

1

2

4

4

1

2

3

3

3

3

2

2

2

2

2

= grid cell resolution

The higher the resolution (smaller the grid cell), the higher the precision, but the greater the cost in data storage

Raster Data:

ArcGIS

Data Compression

Common Methods:

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

Run Length Encoding and

Value Point Encoding

Map Algebra and Cartographic Modeling

A raster modeling language, and an approach to GIS analysis design, developed by J.K. Berry and C. Dana Tomlin in the late 1970s - early 1980s.

It now forms the basis for grid-based analysis in ArcInfo (GRID and Spatial Analyst) and other GIS packages.

Map Algebra

A set of formally defined manipulations on raster data.

Operators: Fundamental mathematical and logical operations on raster data

Functions: Complex combinations of operations

Functions: Types

Higher order data manipulations on raster grids built from the more basic operators.

Local: compute on single-cell basis

Focal: compute on a neighborhood

Zonal: use zones derived from a separate grid for evaluation

Block: like zonal, but the result is assigned to an entire ‘block’ of cells

Global: compute on the entire grid

Functions: Local – Single Values

Functions: Local - Mean

Functions: Focal – Immediate Neighborhood

Functions: Focal – Majority

MinMean

Functions: Zonal – Entire Zones

Functions: Zonal - Max

Functions: Global - Distance

Program Control: Statements and Programs

Statement: notation to represent operations and functions

e.g. NEWLAYER = LocalFUNCTION of FIRSTLAYER and SECONDLAYER

Program: notation to represent a procedure; i.e. a sequence of statements in which each statement operates on the result of a previous statement

Program Control: Programs

Program Control: Programs

Program Control: Programs

Program Control:

Programs

Program Control: Programs

Cartographic Modeling in ArcInfo: ModelBuilder

Locating Suitable Sites for a Waste Dump

Cartographic Modeling in ArcInfo: ModelBuilder

Cartographic Modeling in ArcInfo: ModelBuilder

Cartographic Modeling in ArcInfo: ModelBuilder

Cartographic Modeling in ArcInfo: ModelBuilder

Cartographic Modeling in ArcInfo: ModelBuilder