Data manipulation overview

The first step in creating the citywide walking network was to create a base walking network as shown in figure 14.1. The base walking network was created using road centreline data (part 1 of figure 14.1). All road centrelines that ran through rural land, mostly on the outskirts of a city, were omitted from the process as it is unlikely pedestrians would use a rural road for commuting or for access to public transport. In addition to this, rural roads do not generally provide pedestrian facilities such as footpaths. It is the existence of a formed footpath that defined if a walking link was created, ie walking on the road did not meet the walking quality threshold for the provision of a walking link.

In order to best represent the location of footpaths at a citywide scale, a buffer was created around each road link using the road hierarchy to estimate road width (part 2a of figure 14.1). The relationship between road width and hierarchy for the Christchurch walking network was obtained from the Christchurch city plan (Road hierarchy standards, volume 3: part 8, appendix 2).

The buffer polygons were converted into polylines and then planarised in ArcGIS to ensure connectivity (part 3 of figure 14.1). The planarise tool in ArcGIS splits and connects all line feature segments together by creating intersections at all points where paths originally crossed but did not intersect. Planarising has the effect of reducing complex 3D networks or unstructured linear data into simple, fully connected 2D networks. These line segments became the basis for the creation of the footpath and road crossing network edges.

Figure 14.2 displays an example of the Christchurch base walking network layer on top of an aerial photograph.



Figure 14.1   Steps Involved in creating the base walking network

 


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Figure 14.2   Base walking network – Riccarton, Christchurch city

 

Two attribute fields were created for the walking network edges. One defined the link type and another defined road crossing or intersection type for links that crossed roads.

Links that crossed the road were identified by intersecting the network edges with the original street centreline dataset to identify which edges crossed the road centreline. Each walking link in the base network was identified with a type attribute of FOOTPATH. Link type and intersection attribute values used in the walking network are detailed in appendix D.