Lecture 3: Network Data Models
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Transcript of Lecture 3: Network Data Models
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Department of Geography and Urban Studies, Temple University
GUS 0265/0465Applications in GIS/Geographic
Data Analysis
Lecture 3: Network Data Models
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Representing and Analyzing Networks in GIS
Network: a system of linear features connected at intersections and interchanges
A network is composed of a set of nodes and a set of spanning directed links.
Each link is represented by an ordered pair of nodes (i,j).
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An Example Network
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Examples of Networks
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Node-Node Adjacency Matrix
• The rows and columns in the matrix correspond to the nodes on the network.
• A non-zero element in the ith row and jth column in the matrix represents the numerical value associated with link (i, j).
• A zero element in the matrix in the ith row and jth column in the matrix indicates that there exists no link going from node i to node j.
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Node-Node Adjacency Matrix
0 4 5 0 0 0
0 0 0 8 3 0
6 0 0 7 0 6
9 0 0 0 2 0
0 5 0 0 0 0
0 0 8 0 0 0
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Forward Star Representation
• Links are numbered in the following order:
• First links emanating from node 1 are numbered, then those from node 2, and so forth.
• Links emanating from the same node are numbered in an arbitrary fashion.
• Once this list of ordered links is obtained, data associated with the links are stored in single arrays sequentially.
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Link No.
Starting-node
Ending-node
link-length
1 1 2 4
2 1 3 5
3 2 4 8
4 2 5 3
5 3 1 6
6 3 4 7
7 3 6 6
8 4 5 2
9 4 1 9
10 5 2 5
11 6 3 8
Forward Star Representation
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Forward Star Representation
Corresponding node Element value
1 1
2 3
3 5
4 8
5 10
6 11
link No.
Starting-node
Ending-node
link-length
1 1 2 4
2 1 3 5
3 2 4 8
4 2 5 3
5 3 1 6
6 3 4 7
7 3 6 6
8 4 5 2
9 4 1 9
10 5 2 5
11 6 3 8
Node Pointer Table
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Reverse Star Representation
Forward star representation facilitates accessing links by beginning nodes
Reverse star representation facilitates accessing links by ending nodes
Incoming links at each node are numbered sequentially
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Reverse Star Representation
•
link No.
Starting-node
Ending-node
link-length
1 3 1 6
2 4 1 9
3 1 2 4
4 5 2 5
5 1 3 5
6 6 3 8
7 2 4 8
8 3 4 7
9 4 5 2
10 2 5 3
11 3 6 6
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Reverse Star Representation
Node Pointer Tablelink No.
Starting-node
Ending-node
link-length
1 3 1 6
2 4 1 9
3 1 2 4
4 5 2 5
5 1 3 5
6 6 3 8
7 2 4 8
8 3 4 7
9 4 5 2
10 2 5 3
11 3 6 6
Corresponding node Element value
1 1
2 3
3 5
4 7
5 9
6 11
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Forward and Reverse Star Representation
•
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Network Representation
in ArcInfo
1. Composed of Edges and Junctions
2. Geometric Network stores coordinates
3. Logical Network stores connectivity
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Network Representation in ArcInfo
Solver: a program to perform network analysis
Trace: a solver that traces along a network
NetFlag: a location on a network
Weights: weighting travel along an edge