Network analysis - Spatial Data Analysis: An Introduction for GIS Users - page 85

readers can explore the application of the selected methods. Guidance notes are also pro-
vided on the website to outline how the methods are applied in these particular cases.
h e data used in this case study represent the street layout of the town of Aberystwyth,
captured from historic maps as part of a project exploring the morphology (i.e. the
shape) of various medieval town plans in England and Wales 1 (Lilley et al. , 2007). In
this case study, the objective was to identify the shortest path between the start and
end points indicated in Figure 6.3. Such problems are common, for example any road
user may wish to identify the shortest route between their starting point and their
destination. Information on toll costs, trai c density, and other issues that may af ect
the choice of route can easily be taken into account. ArcGIS™ Utility Network Analyst
of ers a routine to compute shortest paths along networks and this sot ware was used
to identify the shortest path, which is indicated by a heavy line in Figure 6.3.
With an ei cient approach like Dijkstra's algorithm, it is possible to rapidly compute
shortest paths while taking into account factors such as trai c jams where such
information is available.
Summary
This chapter introduced a variety of approaches to characterizing networks which may
have application in, for example, transportation planning contexts. An algorithm for iden-
tifying shortest paths was also outlined. Brief summaries of some important network
analysis problems were also provided. This chapter provides a foundation for under-
standing a major class of approaches for the analysis of vector data, and it presents the
basic principles that are then foundations of a range of methods frequently applied to
solve real-world problems. The suggested further reading provides a way forward if
these kinds of approaches are of interest.
Further reading
Wise (2002) details some algorithms for network analysis. That topic provides a good
starting point for readers wanting to know more about GIS algorithms as a whole. Further
accounts of network analysis are provided by Chou (1997) , Lee and Wong (2000) , and
Chang (2008) . Taaffe et al. (1996) provide an in-depth account of transportation geography
that provides the context for the material covered in this chapter.
This chapter was concerned with line features and their analysis; the analysis of
point patterns (i.e. sets of point 'events') is the subject of the following chapter.
1 http://www.qub.ac.uk/urban_mapping/