Exercise 1: Healthsite distribution in Saint Louis region#
Aim of the exercise#
Become familiar with different types of spatial analysis and geoprocessing tools. Understand the process of discovering relationships and connections between features in spatial data.
Links to Wiki articles#
Data#
Download the datasets here and unzip the files.
Hint
All files still have their original names. However, feel free to modify their names if necessary to identify them more easily.
Task#
The goal of this exercise will be to assess the healthsite distribution in the Saint Louis region in Senegal and which healthsites are prone to flooding.
Hint
The projected coordinate system for Senegal is EPSG:32628 WGS 84 / UTM zone 28N
Load the healthsites layer (
sen_healthsites.shp
) and the administrative boundary data (sen_admbnda_adm1_1m_gov_ocha_20190426.shp
) into your QGIS project. Add OpenStreetMap as a background layer (Hint: XYZ via the browser window or the QuickMapServices plugin).Make sure to reproject the dataset with the administrative boundaries and the dataset with the healthsites into UTM zone 28N. Use the tool
Reproject layer
for this process. See the Wiki entry on projections for further information.Select all healthsites which are located within the Saint Louis region:
Select the region
Saint Louis
in the boundary layer. You can just manually select the specific rows. See the Wiki entry on spatial queries for further information.Save the selection under the new name
Saint_Louis_region
in an extra layer. This can be done by right clicking on the boundary layer –>Export
–>Save Selected Features As...
Use the
Select by location
orClip
tool to select all health facilities within theSaint_Louis_region
layer.Save the new selection under the new name
healthsites_Saint_Louis
in an extra layer (Hint: right click on layer, Export, …).
Investigate the flood risk in Saint Louis. Following the successful selection of all healthsites in the Saint Louis region in the previous step, proceed to load the flood extent layer of Saint Louis into QGIS:
Add the flood extent layer (
EO4SD_SAINT_LOUIS_FLOOD_2018.shp
)While the layer does not cover the entirety of the Saint Louis region, it extends beyond Saint Louis in the north. Utilize the
Clip
tool to clip the flood extent layer to the Saint Louis region (Hint: as input use Saint Louis flood extent, use Saint_louis_region as the overlay) for a more concentrated focus on central Saint Louis. See the Wiki entry on Geoprocessing for further information.Save the selection as
Saint_Louis_flood_clipped
.
When looking at the attribute table of the
Saint_Louis_flood_clipped
layer (Watertype column), you will see that the layer includes flooded, non-flooded and water body areas. Visualize only the flooded areas and water bodies in the dataset:Go into
Symbology
and change the first selection from “Single symbols” toCategorized
.Select the column
Watertype
and clickClassify
.Choose different colors for both the water bodies and the flooded areas. Leave non-flooded areas unmarked or make them transparent (opacity = 0%).
Visual exploration: Which areas are more and less prone to flooding?
Assess which healthsites are prone to flood risk.
Make use of the
Select by expression
tool to select all flooded areas in theSaint_Louis_flood_clipped
layer. You can access this tool through the attribute table by clicking on this symbolSave the selection in a separate layer. Name it
Saint_Louis_flooded_areas
.You can now remove the
Saint_Louis_flood_clipped
layer to avoid confusion.Make use of the
Select by location
tool to assess which healthsites are prone to flooding because they are located within the flooded areas in Saint Louis (Hint: Select features from:healthsites_Saint_Louis
; By comparing to:Saint_Louis_flooded_areas
).Check the attribute table of the
healthsites
layer for the selected features were one pharmacy and one hospital should be selected.
Which healthsites are located close to flooded zones?
Create a buffer around the healthsites in Saint Louis with a distance of
20 meters
. See the Wiki entry on Geoprocessing for further information.Make use of the
Select by location
tool to assess which buffers intersect with the flooded areas.How many healthsites are selected? Check the attribute table. The selection should include five pharmacies and one hospital.
Feel free to experiment with additional buffer distances.
Hint
At this stage at the latest, you will be reminded to reproject your layers. Meaningful buffers can only be calculated in projected coordinate systems. The projected coordinate system for Senegal is EPSG:32628 WGS 84 / UTM zone 28N