Topic 11: Network Analysis

Question 1

Define a network and its components

Answer 1

• A network is a system of linear features that has the appropriate attributes for the flow of objects
• origins in a branch of mathematics known as graph theory

Question 2

two types of network models in ArcGIS

Answer 2

Utility (geometric) networks
- used to model networks where the agent or commodity using the network has no control over the direction
- used to model things like power utility networks, pipeline networks, stream networks and their drainage basins

Topological networks (aka network datasets)
- requires explicit topological relationships to be established
- agents have choice in the direction of travel (although constraints can still be imposed to system)
- used to model things like road networks, rail networks, trail system in a park

Question 3

Components of utility (geometric) networks

Answer 3

• simple networks of nodes and edges that represent network-shaped geographic features
• don’t require embedded topology (eg., can use shapefiles for analysis) - spatial relationships can be computed on the fly

Question 4

Components of transportation networks (network datasets)

Answer 4

• model the movement of agents that have free-will as they travel through the system
• topological relationships relating to connectivity are carefully modelled in such systems
• defined as a series of edges, junctions, and turns

Question 5

What is an impedance matrix?

Answer 5

• To understand patterns of flow in the network, the GIS uses the network graph to construct an impedance matrix = the total impedance along any route can be easily determined as the sum of impedances along all edges travelled

Question 6

Types of network analysis: shortest path (optimal routing)
- definition
- issues

Answer 6

• Routing: find the quickest, shortest, or most scenic route from one location to another
• Travelling salesperson problem: a set of points must be visited - so what is the most efficient order? (vehicle routing problem solver)
• Another class of geographic problems involves the location of optimization of routes through a network (number of possible routes increases very quickly, so algorithms adopt heuristics to solve these problems more quickly)

Question 7

Types of network analysis: closest facility
- definition

Answer 7

• find the closest police car to a crime area, taxi to a fare, ambulance to an emergency, etc.

Question 8

Types of network analysis: Origin-destination (OD) cost matrix
- definition

Answer 8

• define a cost matrix for travel among multiple locations (eg., airline networks, Amazon ground fleet distribution networks)

Question 9

Types of network analysis: service areas/ accessibility
- definition

Answer 9

• find service area around any location on a network