Page Comparison

...

1. A situation in which the density of artificial bridges to be corrected is low (as indicated in red in the figure below, road in green and river in white). In this case, the user should open the merged land cover, the road and the hydrographic network layers in a GIS software and:
   1. Generate a buffer with a radius equivalent to 1.75 time the resolution of the original land cover grid (in light blue in figure b below);
   2. Put the hydrographic network layer in the editing mode and move the concerned segments outside of the buffer area as presented in figure c below (highlighted blue line). You might also want to adjust the way the hydrographic network cuts the road network by placing them perpendicularly as also shown in figure c below;
   3. Save your edits, import the new layer in AccessMod and run the merge land cover tool once again. The new resulting merged land cover should then look like presented in figure d below. 

   

   2. A situation in which the density of vertex on the segments to be corrected is dense (indicated in red in

   Caption ref
   anchor hydr_correc

   a figure a below, road in green and river in white). In this case, open the merged land cover, the road and the hydrographic network layers in a GIS software and:
   1. Generate a buffer with a radius equivalent to 1.75 time the resolution of the original land cover grid (in blue in

      Caption ref
      anchor hydr_correc

      b figure b below)
   2. Put the hydrographic network layer in the editing mode and add a new river segment outside of the buffer area as presented in

      Caption ref
      anchor hydr_correc

      c figure c below (light blue line)
   3. Save your edits and run the first module of AccessMod. The new resulting merged land cover should then look like presented in

      Caption ref
      anchor hydr_correc

      d figure d below

...

...

It is important to be aware that the choice of a coarse resolution can generate the merging of separate road segments that are close to each other. This is shown in

Caption ref
anchor raster_roads

below the figure below where there are artificial intersections between road segments at low resolution (larger grid size). Unfortunately, no correction can be made in this case.

...

Users also need to be conscious of the impact that the change in resolution has on the travel time in cell where patients are reaching the road network.

...

In addition to the above, the rasterization of elongated water body polygons (and other barriers to movement stored as polygons) does not always generate continuous surfaces, unlike when rasterizing vector lines. Figure 5 below provides an illustration of such a problem. As we can see in

Caption ref
anchor raster_elong

cfigure c below, working with lower resolution (larger grid sizes) will create discontinuities, therefore generating artificial bridges in these areas.

...

The solution to address this problem is to:

...

It is important to have a clear understanding of the level of accuracy of the different geospatial data used for the analysis. As can be seen in

Caption ref
anchor catchm_rivers

belowthe figure below, a facility located on the wrong side of a river will lead to the design of a completely different catchment area and therefore contribute to a different population coverage.

...

In view of the above, working at the highest resolution possible would seem to be the best option. Nonetheless, it is important to remember that increasing the resolution of the raster layers results in an increase of the size of the files and the required computational time (see section 3.2.5).

...