A4.3 Results and testing

The results of the calculations are shown with varying degrees of interpolation in figures A.10, A.11 and A.12. Figure A.10 demonstrates an aggressive level of interpolation and hence provides the finest grained output. In contrast figure A.12 shows a more relaxed interpolation and consequently displays flattened contour lines.

Figure A.10   Christchurch meshblock accessibility to GPs, aggressive interpolation

Untitled-1Figure A.11   Christchurch meshblock accessibility to GPs, moderate interpolation


Figure A.12   Christchurch meshblock accessibility to GPs, relaxed interpolation


An analysis was performed on the same result set including geodemographic data to compare the accessibility of Christchurch with the 2007 DfT accessibility values. The population of each meshblock was used to perform a threshold analysis for accessibility to a primary health care provider by private vehicle.

Accession calculated 100% of the population of Christchurch has access to a primary health care provider by private vehicle within 15 minutes. As a general comparison, the UK DfT indicator ‘Percentage of households within 15 and 30 minutes of a GP by public transport/walking’ for 2007 was measured as 98.3%. No meaningful comparison can be made between these two indicators because they relate to two different modes. The UK uses public transport and the simplified Christchurch model uses private motor vehicle. Therefore as a sensitivity test, a five-minute threshold was used which showed 99% of the Christchurch population has access to a primary health care facility by private vehicle.

This analysis demonstrates the use of meshblocks for geodemographic data. Christchurch shows little difference in levels of accessibility when using a modified DfT indicator. The use of individual household data would enable a more detailed accessibility analysis to be undertaken given the finer grained nature of walking, cycling and public transport networks compared with the private vehicle network.

Even so, this assessment may still be limited because the average vehicle speed was set to the UK default of 49km/h. The assumption of such a high constant speed through an urban road network does not reflect the real world situation where intersections, deceleration, acceleration and congestion delays reduce average speeds significantly from posted speed limits. The average vehicle speed reflective of an urban environment is probably closer to 30km/h.