Methodology

Modus Operandi > Buffering the Road Network

     As discussed earlier people do not live on roads and the GVRD residential layer provides us with a more comprehensive classification scheme which can be modified to fit our needs. Therefore, removal of the roads is an important aspect in order to represent population density more accurately. The DMTI spatial dataset contains a file consisting of a comprehensive road network which includes expressways, principle highways, secondary highways, major roads, local roads, ferry routes and trails (Figure 3). For the purposes of this project, since we are focusing only on the Vancouver Central Metropolitan District (CMA), all roads and highways outside of this area are removed.

Figure 3
Figure 3

    After removal of the road network outside of the Vancouver CMA, we are left with the following road types: Expressway, Principle Highways, Major Roads (Figure 4) and Local Roads (Figure 5). In order to take into account the different widths of the different road types, a process of buffering the roads was undertaken. For the expressway, a buffer of 20 meters per side was chosen after examining Highway 1 on air photos. The same process was used for the Principal Highways, Major Roads (Figure 6), and Local Roads (Figure 7), resulting in buffers of 12, 8 and 5½ meters per side, respectively. Due to the large number of features in the local roads layer within the Vancouver CMA, the shear size of the file required us to separate it into 9 separate files in order to complete the 5½ meter buffering of this layer.

figure 4
Figure 4		 figure 5
Figure 5
figure 6
Figure 6		 figure 5
Figure 7

Modus Operandi > Removal of the Road Network

     With the roads now buffered, the GVRD Residential layer can now be modified to more accurately reflect the areas that people live in. A simple clipping procedure was used to erase the buffered roads from the residential layer as well as the agriculture layer. The agricultural layer is included in this analysis because there are many postal code points with population data that fall outside the residential polygons; in this agricultural layer, people do reside on this land and since densities in this area will be small, it is taken into account in calculating total population density.

 

 

Modus Operandi: Introduction . Land Use Preparation . Buffering the Road Network
                        Removal of the Road Network . Manual Editing with Aerial Photography
                        Postal Codes and Spatial Joins . Centroids & Density

 

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