The referral analysis allows one to compute the travelling times and/or the distances along the least-cost paths (i.e. path between two locations that minimizes the total travel duration for those travelling along it, see L’analyse de référence permet de calculer les temps de trajet et / ou les distances le long des trajets de moindre coût (c’est-à-dire un trajet entre deux lieux qui minimise la durée totale du trajet pour ceux qui le parcourent, voir Ray and Ebener, 2008) between two groups of health centers. Such path is different from a straight line as it does take into account the landscape constraints together with the modes and speeds of travel of the population.
For example, one would want to know the distance and travel time between each primary health care facility and the nearest referral hospital in a given Province, or make sure that the travel time between each Basic Emergency Obstetric Care facilities (BEmOC) and the nearest Comprehensive Emergency Obstetric Care facilities (CEmOC) is below 2 hours in a given country.
Starting with entre deux groupes de centres de santé. Ce chemin est différent d’une ligne droite car il prend en compte les contraintes du paysage ainsi que les modes et les vitesses de déplacement de la population.
Par exemple, on voudrait connaître la distance et la durée du trajet entre chaque établissement de soins de santé primaires et l’hôpital de référence le plus proche dans une province donnée, ou s’assurer que la durée du trajet entre chaque structure de soins obstétricaux d’urgence de base (SONUB) et la plus proche structure de soins obstétricaux d’urgence complets (SONUC) est inférieure à 2 heures dans un pays donné.
À partir de la version 5.3.2 of d'AccessMod, the scaling up module has been improved to run in parallel mode, which means it can take advantage of all CPUs that are allocated to the AccessMod Virtual Machine. This speeds up the referral computation (see details in Appendix 5). If you are running a referral analysis with a large number of facilities, it is therefore better to first set up your Virtual machine with a maximum of CPUs and memory (see le module de mise à l'échelle a été amélioré pour fonctionner en mode parallèle, ce qui signifie qu'il peut tirer parti de tous les processeurs alloués à la machine virtuelle AccessMod. Cela accélère le calcul de la référence (voir les détails à l’Annexe 5). Si vous exécutez une analyse de référence avec un grand nombre de ressources, il est donc préférable de configurer d'abord votre machine virtuelle avec un maximum de processeurs et de mémoire (voir Section 4.2).
In the following exercise, you are going to compute the travel times and distances between the "Health centers" and the "hospitals" from the demo dataset.
The following two screenshots explain how to fill the sections used to input the different layers and parameters to run the analysis:
Data inputsDans l'exercice suivant, vous allez calculer les temps de trajet et les distances entre les "centres de santé" et les "hôpitaux" à partir du jeu de données de démonstration.
Les deux captures d'écran suivantes expliquent comment remplir les sections utilisées pour saisir les différentes couches et paramètres permettant d'exécuter l'analyse:
Données en entrée:
(1) Under “Select merged land cover layer (raster)”, select the raster format layer containing the merged land cover, "land cover merged". Under “Select scenario table (table)”, select the travel scenario table you want to use. The one created in the previous module in the present case
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(5) In the same menu, under “Select facility ID field (unique)” and “Select facility name field (text)", Select the field from the attribute table of the "To" health facility layer that contains the unique identifiers as well as the field containing the name of each hospital.
Travel scenarioScénario de déplacement:
(6) Like for the accessibility analysis (see Section 5.5.3), this section is used to either import the content of the external scenario table and/or manually modify the information reported in the label, speed and/or mode columns. We will just keep the same values as before for this exercise.
The sections in the second part of the analysis panel can then be filled as follow:
Facilities selection
Sélection des structures de santé
(1) In the “From” table, select the facilities you want to serve as points of departure ("From"). You can either do it “by hand”, by checking the records that have the value “Health Centre” in the column “hf_type”, or you can use the filter tool at the top of the table to automatically select these centers. The second option is particularly useful when there is a large number of facilities in the layer and/or to be selected.
(2) Similarly, in the “To” table, select the facilities you want to serve as points of arrival ("To"). That means that those facilities that have the “Hospital” type in the column “hf_type”, are selected for the present exercise.
Analysis settingsParamètres d'analyse:
(3) Under “Type of Analysis”, select the option to do an anisotropic analysis as you did for the previous analysis
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(6) Under “(Add short tags)”, give short tags to be attached to the different outputs of the analysis. We will use "referral" for the present exercise.
Validation:
(7) 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.
A transparent window with some text and a progress bar will appear in front of the panel while the analysis is being conducted. Please wait until this window disappears to continue using AccessMod. This analysis can take a lot of time to completed especially if the number of health facilities to be processed is high.
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