Catchment Generator


The Catchment Generator tool is a set of routines that are capable of creating polygon “catchments” (hereinafter used to refer to any polygon data set that will act as the basis for walkability analysis) on a feature-by-feature basis around a user selected point data set. The generated polygons are street network buffers (rather than radial buffers) based on the user supplied parameters of maximum distance along the network to traverse and a buffer value which will dictate the width of the buffer around the traversed network segments.


To show the catchment generator tool in use we will run it for the Inner East of Melbourne, generating catchments around train stations.

To do this

  • Select Melbourne Inner East SA3 as your area
  • Select the following datasets
    •  PSMA Street Network (you only need to select the blue Geometry attribute
    •  PSMA Railway Stations (again, you only need to make sure the blue Geometry attribute is selected)

Once you have added these datasets, open the Catchment Generator tool (Tools  Walkability  Catchment Generator) and enter your parameters as shown below. These are explained below the image

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  • Road Network: Line data set representing a road or pedestrian network. We select PSMA Street Network in this instance
  • Points of Interest: Point data set representing the locations to be analysed.  The data set should contain an attribute to act as a unique identifier for the remainder of analysis steps. These points can either be retrieved from the AURIN portal federated databases, uploaded to your own session, or even drawn using the drawing tool. We select PSMA Railway Stations as the dataset for this.
  • Maximum walk distance: The maximum distance (in metres) along the line network data to be traversed from each input point. We select 800m for this analysis.
  • Buffer size: The width (in metres) of buffer to be applied to the traversable line, network segments. We select 50m for this analysis.

Once you have entered your parameters click Add and Run to execute the tool.


The output of the Catchment Generator tool will appear in your Data panel, labelled Output: walkability-001… . To visualise this, click the spanner next to it and select Display on Map. This will bring up a dialogue box where you can select colours for the catchments.

Click Update and Display to show the catchments on your map. It should look something like the figure below, depending on the colours you have chosen.

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[Click to Enlarge]

These outputs can be used for the other tools in the Walkability toolkit.



Studies in Australian and the United States have generally created street network buffers based on the distance that could be covered by a person briskly walking for 15 minutes from their residences as a standard definition of a catchment i.e., around 1.6 km.  In GIS terminology these are known as ‘service areas’ or isochrones, which are developed through analysis allowing the software to traverse a linear network (such as a road network or one augmented with pedestrian or bicycle paths) to identify how far a participant can walk in all directions from their home at a given time at a set speed.

Data Sources

The primary input of this tool is two spatial data sets; One shapefile which represents the locations for which walkability metrics are to be calculated (e.g., study participants residential locations) and one shapefile of a line data set representing a network, such as a road data set.

The point data set may be of users own creation, generated from a set of addresses which are “geocoded” to a spatial location matching the street address. At the time of writing, tools to geocode addresses were not available in the AURIN Portal, thus users who do not have address data already spatially represented in a shapefile will need to find a service elsewhere to do so.

Past work at CBEH on the Perth metropolitan area, used a road centre line data set sourced from the spatial data agency Landgate as the basis for generating catchments in the ESRI’s ArcGIS software. That data was cleaned to remove or remedy the following:

  • Remove freeway road segments (not considered to be traversable by pedestrians);
  • Removal of yet to be constructed road segments based on an audit against aerial photography;
  • Close undershoots found in “unconnected” road segments;
  • Remove redundant road segments that were functionally part of another road or were part of cartographic representations of a road feature but over represented the number of road connections.  This was especially applicable to roundabouts in the data set.

Tools to perform the cleaning options listed above are not provided in AURIN Portal.  As part of the diagnostics for this project, analysis was conducted to compare the results of a cleaned road data set compared with the nationally available road data set provided by PSMA for use in the AURIN Portal (click here for more information on this data).  It is recommended that users assess the amount of street network validation and correction they do based on the level of accuracy they require.

Analysis Process

Network analysis uses graph theory to examine how a network can be traversed to access all possible network segments up to a range specified by the user.  In an iterative manner (point by point) this is done to create a set of line segments from the origin point.  These lines segments are then traversed by a distance specified by the user (Maximum walk distance) from the sample point.  The line segments that can be traversed are then buffered by a user specified distance (Buffer size).