Department of Geography and Urban Studies, Temple University

GUS 0265/0465Applications in GIS/Geographic

Data Analysis

Lecture 3: Network Data Models

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).

An Example Network

Examples of Networks

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.

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

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.

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

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

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

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

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

Forward and Reverse Star Representation

•

Network Representation

in ArcInfo

1. Composed of Edges and Junctions

2. Geometric Network stores coordinates

3. Logical Network stores connectivity

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