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Captioneditem
anchorraster_elong
captionImpact of rasterization on elongated polygons (a) for a resolution of 180 meters (b) and 1 kilometer (c).


The solution to address this problem is to:

  1. Convert your polygon water body layer into polyline.
  2. Merge the polyline resulting from step 1 with your line format barrier layer (see section 3.3.1.8 for details).
  3. Use both the original polygon layer and the merged line layer as barrier when creating the merged land cover layer in AccessMod.

At the same time, working with low resolution raster format data might lead to some health facilities to be located in a “No Data” area (river network for example). If this happens, the user will have to manually move the facility to the nearest cell. The user should be very careful to move the facility to the correct side of the river/water body. This modification of the location can be considered as an adjustment to the resolution used in the analysis, and its impact on the results of the modelling should typically be very small.

Accuracy

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

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anchorcatchm_rivers
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.

Image Added

Captioneditem
anchorcatchm_rivers
captionExtent and corresponding population (values within the boxes) for two catchment areas (dark blue (6165) and green (6031) lines) when the facility is placed on a different side of a river (light blue)