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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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 Next, data can be entered for the second part of the analysis panel, as follows:

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Analysis settings:

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(2)  Direction of travel: Select the direction of travel of the patients. Please note that this field will only appear if the "anisotropic" option has been selected above. For the purpose of the exercise, choose "Towards facilities".

(3)  

(4) Facilities processing order: The geographic coverage analysis is done in a sequential processing order: one health facility is considered and processed, and then the next facility is considered, and so on, until all health facilities have been processed. At each iteration, the population identified as belonging to the computed catchment of a specific health facility is subtracted from the overall population layer. Such a processing order allows AccessMod to simulate both the saturation of services in populated areas and/or potential patient preferences when patients are within reach of many different health facilities. For this reason, the order in which individual health facilities are considered within the analysis can influence the results (although it is very difficult to predict how). Please see Annex 4 for details of how this analysis is done.

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- "The population living within a circular buffer around the facilities": by giving a circular buffer radius (in meters), AccessMod will first compute a circular buffer around each health facility, determine the population living in each of these buffers, and use these figures to determine the processing order for the health facilities. Again, this approach would give precedence to facilities located in densely populated areas.

(45) The field appearing in this step will change depending on the processing order option selected under step 3, namely:

• "Select field from the facility layer": this field appears if you have selected "A field in the health facility layer" option under step (3). In this case, select the field from the health facility layer that contains the integer values you want to use for defining the processing order - this option is being used for the exercise followed here and the field containing the maximum coverage capacity has been chosen in this case.
• "Given travel time [minutes]": this field appears if you have selected "The population living within a given travel time from the facilities" option under step (3). In this case, enter the travel time in minutes to be used by AccessMod to compute the extent of the catchment area for each health facility.
• "Buffer radius [meters]": this field appears if you have selected "The population living within a circular buffer around the facilities" option under step (3). In this case, enter the radius in meters to be used by AccessMod to compute the extent of the buffer for each health facility.

(56) "Processing order": Select here the processing order based on the option that has been selected under point 3. For the purpose of the exercise, select a descending order, in order for AccessMod to first process facilities with the highest maximum coverage capacity.

(67) "Maximum travel time [minutes]": specify the maximum travel time (in minutes) that should be used by AccessMod to define the maximum reach of the catchment area attached to each health facility. For the exercise, specify 120 minutes.

(78)  "Options": Several additional options are available:

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Advanced options "Optimize dynamically computation according to the scenario":  this option decreases the computation time, particularly when the number of cells is large, that is when the extent of the zone is large and at high resolution. The optimisation procedure clips all raster around each facility, with clip surfaces corresponding to the maximum surface of a catchment that would be computed by using the largest speed found in the travel scenario and applied everywhere. It is recommended to use this option with the geographic coverage analysis.

(89) 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.

Facility selection

 (910)  As in the previous analysis, you can select the set of facilities for which the analysis will be performed. Keep all facilities selected for the exercise.

Validation:

 (1011) The validation module should indicate that all fields have been correctly filled in (with a green “OK”). If this is the case, you can hit the "Compute" button to launch the analysis. If this is not the case, the "Compute" button will still be in red and you will have to go through the warning and error message to find out what needs to be adjusted.

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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).
• amRankValues_capacity: values for the parameter used to define the processing order. In the present exercise, this column 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.
• amRankComputed: processing order applied during the analysis based on the content of the "amRankValues_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.
  
  
  

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