Geog 303 - Introductory GIS

Week 9 Lectures

Network analysis

A network is a system of connected linear features through which resources flow. Some examples of features and resources are as follows:
 
Linear Feature
Resource
streets vehicles
pipes water, sewage
power lines electricity
railroad trains
water channels water (drainage)
telephone lines phone calls

Elements of a network

Links
Links are the conduits for movement.
Attributes: - two way impedances such as time or rate of flow
- demand such as students, customers, water, electricity, etc.Barriers
Barriers prevent movement between links.
Turns
Turns indicate all possible turns at an intersection of links.
Attributes: - impedance such as turning time or turning flow rate
- restrictions such as no left turnCenters Centers are locations which receive or distribute resources; for example, schools, fire stations, and reservoirs.

Attributes:

- resource capacity such as student enrolment, parking spaces, and water volume
- impedance limit such as maximum distance or time between a center and a linkStops Stops are locations on a route to pick up or drop off resources; for example bus stops, newspaper dropoff points, warehouses

Attributes:

- demand for resources to be transported along the links, such as students, products, commuters, etc.
 (adapted from ESRI documentation on networking)

Example of attributes used in network analysis

These network elements contain both spatial and attribute components which must be represented and analysed using network-specific operations which simulate network characteristics and functions. An example of attribute data included for a street network might be:
traffic speed
travel time
distance
intersection conditions
type of intersection control (eg. traffic lights, stop sign)
time-of-day
road construction
stop-over (parcel delivery)
number of turn-offs
etc...

Main network functions

Routing
- route resources along an optimal path
eg. from fire station to fire
from current location to scene of accident
from warehouse to customers

-to define the paths the following information is needed:
origin
pass-thru points
stops
destination
Resource Allocation
- allocate resources along linear features to or from centers
eg. students to schools
voters to polling booths
water from reservoirs

- the centers must be defined

- then the resources are allocated to the centers based on such criteria as:

distance to/from center
time taken to get to/from center
capacity of center
Address Matching
- match addresses to locations on streets (and which side of street)
eg. locate customers
site facilities
locate students
site schools
determine market for mailing list/advertising

Applications for networking

The various types of applications of network analysis include the following and are provided with some examples.
Routing
bus routes
pedestrian routing
rubbish collection routes
 
Emergency Services
evaluate potential emergency vehicle sites
route emergency vehicles
evacuation plans (disaster/planning)
 
Districting
determine polling locations
analyse distribution of goods to customers
 
Facility Siting and Design
calculate service and parking demands for libraries, shopping centers, airports, etc.
utility companies analyse customer requirements/usage
 
Natural Resources Management
water availability and distribution
simulate water pollution and analyse downstream effects
storm runoff
forestry logging plans

 

 

videos on wed, along with a short exercise.
 

 

 

We discussed the URISA Ethics in GIS page. It can be found at http://www.urisa.org/ethics/code_of_ethics.htm