ABSTRACT
The chapter describes the basics of networks, to give a general idea of the type of questions they can be used to answer and to provide an overview of the basic types of network analysis that a Geographic Information System (GIS) can undertake. Using a network can generate more accurate measurements, but also allows for considerations such as cost, time of day, intervening opportunities between origin and destination, and differences resulting from modal choice. Changes to the network can be implemented as barriers - either points, lines or polygons, depending on the type of disruption envisioned - that can be turned on and off to assess changes in routes and speeds. Using the underlying network, the GIS calculates the lowest cost distance between a set of origins and destinations. Location-allocation models appear in a large number of applications of GIS. As a tool, location-allocation is used most often in public sector GIS applications.
