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GENERIC STEP-BY-STEP APPROACH STEP THREE

Pay careful attention to the way in which you define the

scope, objectives and context of the accessibility study.

ACTIVITY 3 – IDENTIFY AND WEIGHT THE FACTORS TO CON-
SIDER IN THE STUDY

In addition to the geographic access standards of your department, there may be other factors or criteria
to consider in determining where service points should be located. These could include the extent of
in- and out-migration, levels of socio-economic development, and the availability of suitable land and
basic services.

One can weight the selected factors to reflect their level of importance. This will assist you in identifying
the geographic areas that should be prioritised for attention. The factors can be weighted in various
ways. For instance:

❏ A nominal weight could be used to increase or decrease the importance of a factor. Areas affected
by out-migration could, for instance, be weighted by a percentage value of -10 while areas with
significant in-migration may be weighted by a percentage value of +50. A nominal weight could
also be used when insufficient quantitative data on the factor is available.

❏ The standard deviation of a factor that can be quantified can be used to define weights. For
example, the frequency of the total number of crimes can be statistically analysed and areas that
fall in the different standard deviations used to weight the target population. Areas falling into
the positive third standard deviation (representing areas with total crimes much higher than the
average) can be weighted up by a certain percentage.

ACTIVITY 4 – PREPARE THE SPATIAL DATA

This activity includes the collection of various datasets as well as preparation of the data for use in a
GIS. You will, among others, require information on your service points, population demographic data
and available road networks. Ensure that the spatial and attribute data of your department are complete,
accurate and up to date to ensure that the results of your accessibility studies are reliable.
Always try to use the most current spatial data. Also ensure that the spatial data is at the smallest spatial
level possible. For instance, data on the target population should prefarably be at a small area level,
which is the smallest geographical area for which StatsSA provides census data.
In preparing the data that will be used in the accessibility study you should focus on
the following six steps:

a) Define the study area.

b) Create a buffer area around the study area.

c) Assess the quality of spatial information.

d) Incorporate the spatial information into accessibility modelling software.

e) Improve the movement network connectivity using Feedlinks and Delaunay networks.

f) If travel time is regarded as a measure of geographical access in your study, you should assign
various speeds limits to the movement network.
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