Investigating geographical differences in the mode of transport to work using circular statistics
For many, the journey to work (JTW) constitutes a habitual activity. The 2001 Census recorded approximately 1.1 million individuals’ journeying to work across the South-East Queensland (SEQ) region of which Brisbane City constituted the largest portion (beginning and ending their JTW).
Mapping flows of geographical phenomena (such as JTW patterns) has been the subject of interest for many years dating back to the work of French engineer Charles Minard and his depiction of Napoleon’s advancement through Russia during 1812-13. Whilst the application of arrows and vector fields has been successfully applied in previous studies mapping flows, it is argued in this paper that such a representation when applied to JTW data creates visualisation issues due to the volume and multi-directional nature of the flows. To overcome this visualisation issue, an alternative approach using a novel combination of circular statistics in a GIS environment is presented.
Circular statistics are first introduced followed by the JTW data that include the total number of journeys between an origin (home) and destination zone (work) by mode of transport across the SEQ region. Using bespoke tools developed in a GIS environment the direction and frequency of each flow is calculated using circular measures and differences between each mode of transport examined.
Analysing the mapped outputs illustrates that there are strong JTW patterns across the SEQ region. Strong patterns, and the embedded directionality and modality are readily detected using a spatial approach that combines outputs derived from GIS and circular statistics.