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Task 3: Larger scale accessibility analyses#

There are two main approaches on accessibility analyses: network and cost raster based. In this task we will use both methods on the example of the country Rwanda. For the network based approach we will use the isochrone API of the openrouteservice to generate catchment areas for 5, 10 and 60 minute ranges. The cost raster approach will be conducted with the saga tool Accumulated Cost which is already part of the QGIS tools through the SAGA provider.

Download all datasets here. Save the folder on your computer. Unzip the .zip file. The unzipped folder is structured according to the recommended folder structure for QGIS projects. Under “data > input” you find the following datasets:

Vectorlayer

  • task3.gpkg

    • rwa_healthcare (points): Hospital locations in Rwanda (based of OpenStreetMap)

    • rwa_adm0_boundary (polygons): Country boundary of Rwanda

    • rwa_adm1_boundary (polygons): Administrative boundaries for the second level of Rwanda. In Rwandas case these are called provinces

    • rwa_adm2_boundary (polygons): Thirs level administrative boundaries of Rwanda. In Rwandas case these are called prefectures

Rasterlayer

Use the following files:

  • motorized.tif : Friction layer for motorized travel profiles

  • Walking.tif : Friction layer for walking mobility profiles

  • population.tif : Population counts from WorldPop

STEP 1: Network - Isochrones#

We start with the isochrones gain. This time for a whole country - Rwanda. Use the layer rwa_healthcare as input point layer and 5, 10 and 60 minutes as ranges.

Click in the toolbar on the ORS Tools plugin Icon Icon. Click on Batch Jobs -> Isochrones from Layer. Leave all settings at default except:

Travel mode

driving-car

Input Point layer

rwa_healthcare

Comma separated ranges

5, 10, 60
Watch here:

STEP 2: Raster - accumulated cost (Requires SAGA)#

Open the Processing Toolbox and scroll down to SAGA choose Raster Analysis and then Accumulated Cost or enter “Accumulated Cost” in the search bar. Leave all settings at default except:

Destinations

rwa_healthcare

Destinations

motorized

Local Cost

motorized
Watch here:

Select the Accumulated Cost output layer and open the Layer styling panel (F7) choose Singleband Pseudocolor. Adjust the range from a minimum of 0 to a maximum of 60 minutes. Overlay the isochrone output layer. Compare the different catchment areas. Add an OpenStreetMap background layer to better understand the differences. May consider dissolving (Vector Geometry >> Dissolve) the isochrone output layer by range value, to get a more clear outline of intersecting ranges in areas with multiple healthcare facilities. Take a look at the Attribute table of the Isochrone output layer. One of the attributes bears information on the population living within the boundary of the isochrone. The population estimates are based on the Global Human Settlement Layer project.

Question

How many people are covered within 5, 10, 60 minutes in Rwanda according to our Analysis? How would you describe the differences? What are the advantages/disadvantages of the raster versus the network approach?