PORTAL USER GUIDE
The Catchment Generator tool allows you to create an area or polygon that extends along a line around a point. The generated polygons are street network buffers (rather than radial buffers) based on the distance along the network (line data) and a buffer value for the width.
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.
The inputs of this tool consist of two spatial data sets; one shapefile which represents the locations for which walkability metrics are to be calculated, for example, the residential locations of the study participants, 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.
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).
Note: The walkability tools work optimally on regions around the size of local government areas. Study areas larger than this may be faced with long processing times.
In this guide, we will use the Australian Children’s Education and Care Quality Authority (ACECQA) data and OpenStreetMap Australia Street Network data to display walkable catchments around daycare facilities for children in Launceston.
First, we set up your area of study:
Select Launceston SA3 (Australia →Tasmania → Rest of Tasmania → Launceston and North East → Launceston) as your area.
Next, we access the data we need to run our tool.
Select the following datasets.
- OpenStreetMap – Lines (Australia) 2017 selecting the following attributes:
- Unique Identifier
- Unique Identifier
- ACECQA – National Register Education Services in Australia (Point) 09/06/2017 selecting the following attributes:
- Unique Identifier
Once you have added these datasets, open the Catchment Generator tool (Tools →Walkability → Catchment Generator) and enter your parameters as follows:
- Road Network: Line data set representing a road or pedestrian network. Select OpenStreetMap – Lines (2017).
- Points of Interest: Point data set representing the locations to be analysed. These points can either be accessed from data connected to the Portal, a point location dataset of your own that you have uploaded to the portal or a set of points you have created in the Portal using the drawing tool. Select ACECQA – National Register Education Services in Australia (Point) 09/06/2017.
- Maximum walk distance: The maximum distance (in metres) along the line network data from each point. We select 500m for this analysis.
- Buffer size: The width (in metres) of buffer to be applied to the line. We select 30m 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 as another dataset in your Data panel, labelled Output: walkability001-points-to-regions.
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 catchment on your map. It should look something like the figure below, depending on the colours you have chosen.