A3.2 Results and testing

The output contour information is based on a generalised distance-based cost. It is important to remember the output describes the accessibility of the destination. The shape of the contour map is a polygon that connects the destination locations. The output from the preceding inputs is shown in figure A.5.

Figure A.5     Graphical output (no modification)

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Very poor accessibility

 

Very good accessibility

 

Very poor accessibility

 

It is interesting to note from the accessibility analysis that destination locations closer to the network and origins have a higher accessibility. This is unsurprising given this is the basis of the accessibility calculation. Where origins and destinations are close together, the accessibility of the destination will be high. What is interesting though is a contour plot, which requires three points to interpolate accessibility, shows large areas that could appear to have no (rather than low) accessibility. This is not correct. As the plot is destination based there are no destinations within these white areas so the contours are not able to be inferred for these locations.

It is also interesting to note there are at least two points close to the network and close to an origin in cells a, b and f, which appear to have very poor accessibility. This is an abnormality because theoretically, these points should have connected to the network. It is unknown why these points did not ‘connect’ to the network.

Trialling variations of the standard analysis and removing two of the central links bordering cells b and e, and d and e, results in a changed spatial pattern of accessibility as shown in figure A.6.

The result is accessibility decreases around the points in cell e where one of the destinations can now no longer connect to the network within the minimum 1km distance specified. This means the destination at the bottom of cell g continues to have high accessibility but the area of very good accessibility has decreased.

Figure A.6     Graphical output (less two links)

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Very good accessibility

 

Very poor accessibility

 

Removed

links

 

Very poor accessibility

 
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Increasing the minimum 1km connection distance to 2km results in the pattern of accessibility changing as shown in figure A.7.

The result is accessibility improves over the whole area as there are now more destinations able to connect to the network. Again, the only abnormality to this is the three points identified earlier in cells a, b and f that are still unable to connect to the network. Even so, accessibility can be seen to have increased, and this difference can be seen when comparing figure A.7 with figure A.6.

Figure A.7        Graphical output (max 2km connection)

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Very poor accessibility

 

Poor accessibility

 

Very good accessibility

 

 

Removing two of the destinations, one in cell e and the other in cell f results in changed accessibility as shown in figure A.8.

The analysis does not differ greatly from the original analysis other than the polygon shape has changed to reflect the removed destinations.


Figure A.8        Graphical output (two destinations removed)

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Very good accessibility

 

Very poor accessibility