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The geographic coverage analysis allows you to take into account the availability of services (i.e. the capacity of health facilities to attend to patients) and to consider this in addition to the physical accessibility constraints, in order to define the catchment area associated with each health facility.

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• "Compute catchment area layer": Select this option if you wish to obtain a vector layer containing the individual catchment areas (polygons) attached to each facility during the analysis. This option is checked by default.
• "Remove the covered population at each iteration": Select this option to remove the population attached to the health facility from the population distribution grid at each iteration. This option is checked by default and should remain as such to avoid that the same population is attached to more than one facility. Un-selecting this option is nevertheless useful if you want to estimate the population located within a given travel time of a set of facilities without account for the overlap between catchment areas.
• "Compute map of population cells on barriers": Select this option to create an output raster file containing the cells in which a population resides but where the cells fall on a barrier. This population will not be taken into account in the analysis, and it is therefore often necessary to modify the input population distribution layer in raster format prior to the analysis to avoid this issue (see Appendix 1). This option is selected by default and you can keep it that way for the present exercise
• "Generate zonal statistics (select zones layer in data input panel"): Select this option to automatically obtain the percentage of population being covered by sub national level zones through the analysis. This option is unselected by default. Once selected, a new field labeled "Select zones layer (vector)" appears in the "Data input" section (see point 8 attached to the previous screenshot) for you to select the layer in question. For the purpose of the exercise, check the box, (select the "zone for stat" layer, "cat" as the field containing the unique ID and "admin_name" as the field containing the zone names).
• "Run the analysis without considering capacities": Select this option to avoid attributing a maximum capacity to centers and to obtain catchments that are only limited by the maximum travel time. This option is unselected by default.
• "Add column with original population sum under each facility's travel time". Select this option to output an additional column named "amPopOrigTravelTime" in the output table "health facility statistics" (see below). This column will give the full population within a facility's catchment, i.e. the population from the original population raster and without any of it being attributed to another catchment.
• "Add the additional columns describing the coverage of the population (total population, effective residual population before and after calculation of the catchment area)". This option adds five additional columns in the output table "health facility statistics" (see below). These can be used to check that the total population and residual population after each iteration are what is expected.

(9) Add short tags:  Indicate short tags to be attached to the different outputs of the analysis. We will use "geographic analysis 120m" for the present analysis. Avoid very long name as it has been found to sometime prevent Excel to open the output generated xls files.

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• cat: unique identifier of the health facility as per to the field selected from the attribute table of the health facility layer.
• name: name of the health facility as per the field selected from the attribute table of the health facility layer
• capacity: maximum coverage capacity of the health facility expressed as the number of people that the facility can serve (as per the field selected from the attribute table of the health facility layer).
• amOrderValues_x: with "x" being the name of the parameter used to define the processing order. The values of this column are the values of this parameter. In the present exercise, this column is named "amOrderValues_capacity" and contains the maximum coverage capacity of each facility as this is the option that was selected above. Please see the boxed note below for more information regarding the label and content of this column when using the other options.
• amOrderComputed: processing order applied during the analysis based on the content of the "amOrderValues_capacity" field and the direction of processing (ascending or descending), as selected by the user.
• amTravelTimeMax: maximum travel time in minutes, as set by the user for the analysis.
• amPopTravelTimeMax: total population located within the maximum travel time set for the analysis (amTravelTimeMax).
• amCorrPopTime: Pearson correlation coefficient between the set of travelling times (t, from 0 to the maximum travel time) and the corresponding covered population within this time step (i.e. the sum of population in all cells that are located between t and t+1 of travelling time). This correlation measure gives a rough estimate of how the population is distributed through space as we move outward from the health facility. As an example, a large positive value (e.g. 0.707 in the third line of the above table) means that the population is relatively uniformly distributed as you expand outwards from the facility. A strong negative correlation would mean that there is more population close to the health facility than there is far away from it. A correlation close to zero means that there is no specific tendency in how the population is spread within the catchment. This correlation should really just be used as a relative indicator, as we do not provide the statistical significance of the correlation (you should use proper GIS analysis outside AccessMod if you need statistical insights about how the population is spatially located within the catchments).
• amTravelTimeCatchment: travel time to reach the maximum extent of the catchment area attached to the health facility. This value is either:
  • Equal to the maximum travel time set for the analysis (amTravelTimeMax) when the maximum coverage capacity of the facility has not been reached within the set time (120 minutes in this example). In the current exercise, this is the case for the Queen Elizabeth Hospital.
  • Smaller than the maximum travel time set for the analysis (amTravelTimeMax) when the maximum coverage capacity of the facility is reached before reaching amTravelTimeMax. This is the case of The Medka Health Centre in the exercise.
• amPopCatchmentTotal: population located within the catchment area for the travel time reported in the amTravelTimeCatchment field
• amCapacityRealised: part of the maximum coverage capacity of the health facility that is being used (realized) based on the total population located in the catchment area for the given travel time. This value is:
  • Equal to the maximum coverage capacity of the health facility (capacity) when this value is reached before the maximum travel time (amTravelTimeMax). An example is the Medka Health Centre in the present exercise.
  • Smaller than the maximum coverage capacity of the health facility (capacity) when such capacity is not reached within the maximum travel time (amTravelTimeMax). An example is the Chiradzulu District Hospital is in this the present exercise.
• amCapacityResidual: part of the maximum coverage capacity of the health facility that is not being used. This value is calculated by making the difference between the maximum coverage capacity (capacity) and the realized capacity (amCapacityRealised). This value is therefore equal to 0 when the maximum coverage capacity is being reached within the given travel time.
• amPopCatchmentDiff: Part of the total population located in the final catchment area (amPopCatchmentTotal) which does not experience facility coverage by lack of sufficient coverage capacity in the health facility. This value is calculated by making the difference between the total population in the catchment area (amPopCatchmentTotal) and the realized capacity (amCapacityRealised). This value is therefore:
  • Equal to 0 when the maximum coverage capacity is not reached within the given travel time
  • Greater than 0 when the maximum coverage capacity is reached within the given travel time
• amPopCoveredPercent: cumulative geographic coverage expressed as a percentage. This value corresponds to the percentage of the initial population distribution grid (i.e. the layer selected in the "Select population layer (raster)" field) that has been covered after having processes the health facility in question.
  
  Additional columns
• If you have selected the option "Add column with original population sum under each facility's travel time", an additional column named "amPopOrigTravelTime" is found in the output table. This column contains the full population within a facility's catchment, i.e. the population from the original population raster and without any of it being attributed to another catchment.
• If you have selected the option "Add the additional columns describing the coverage of the population (total population, effective residual population before and after calculation of the catchment area)", five additional columns are found in the table:
  amPopTotal: contains the total population within the extent of the area considered. It should not change between each iteration. 
  amPopTotalNotOnBarrier: contains the total population found outside of barriers. It should not change between each iteration. 
  amPopTotalOnBarrier: contains the total population found in barriers. It should not change between each iteration. 
  amPopResidualBefore: contains the residual population before the start of the iteration.
  amPopResidualAfter: contains the residual population after the iteration. The loss of population with what is found in the previous column is the population "caught" by the facility's catchment.

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 Zonal Statistics Results

 If If you checked the "Generate zonal statistics (select zones layer in data input section)" in the "Analysis settings", then the analysis will generate one last table containing the distribution of geographic coverage obtained at the zone level after conducting the analysis.

 Once Once opened in Excel, this file (named “table_zonal_coverage_geographic_analysis_120m.xlsx”) in the present exercise, contains the following columns:  

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• cat: unique identifier of the zone, as per the field selected from the attribute table of the zone layer.
• name: name of the zone, as per the field selected from the attribute table of the zone layer
• amPopSum: Total population located in the zone
• amPopCovered: Population being covered through the geographic coverage analysis, therefore attached to the existing health facilities
• amPopCoveredPercent: Percentage of the total population being covered through the geographic coverage analysis

 This This table is particularly useful to identify potential inequities in geographic coverage at the sub-national level. In the current exercise, for example, we can observe important disparities in coverage between zones. One of them even has 0% of geographic coverage (North West).

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