Case study

The accessibility calculation methodology described in the previous chapter was tested by measuring accessibility to different activities from meshblock centroids in the Christchurch city urban area in 2009. It is important to emphasise the case study was undertaken before the devastating Canterbury earthquakes of September 2010 and February 2012. 

The calculations were performed using ESRI’s ArcGIS 9.3 with the Network Analyst extension. All the calculations required in the methodology were implemented using Python 2.5 and the ArcGIS Geoprocessor. This allowed the calculations to be performed outside of the ArcGIS Graphical User Interface, conserving system memory resources.

Due to out-of-memory issues when running Network Analyst, the meshblock centroids data set was separated into a series of subsets. These subsets were then processed one at a time. Once all the meshblock centroids subsets had been processed, the results were merged into a single result layer. By using the Python scripting language to create and call a sub-process to perform each iteration of the network calculations, the calculator was forced to release the memory so that it was available for use in the next iteration.

The sources of the datasets used in the Christchurch city case study are listed in table 16.1.

Table 16.1    Data sources used in the Christchurch city case study

 

Dataset

Source

Destinations

Doctors

Ministry of Health

Hospitals

Ministry of Health

Primary schools

Shapefile of Ministry of Education data – Koordinates.com

Secondary schools

Shapefile of Ministry of Education data – Koordinates.com

Further education

Geocoded by Abley Transportation Consultants Ltd

Convenience stores

Zenbu.co.nz

GeoHealth Lab - University of Canterbury

Supermarkets

Zenbu.co.nz – verified against supermarket websites

Places of employment

Meshblock centroids, with weighting based on number of available jobs. Statistics New Zealand 2006 Census data

Origins

Sites to measure

Meshblock centroids – Derived from Statistics New Zealand 2006 Census data

Land parcel centroids – Derived from Christchurch City Council cadastral data

Networks

Walking network

Abley Transportation Consultants Ltd

Cycling network

Abley Transportation Consultants Ltd

Public transport network

Abley Transportation Consultants Ltd

Private vehicle network

Abley Transportation Consultants Ltd