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As a next step, select the "Accessibility" analysis from the "Analysis" module, and fill the various fields as indicated here:
Data inputs:
Under:
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The columns presenting a label starting with “am” are not coming from the attribute table, but have been generated by AccessMod. These particular columns are the following: - "amSelect": allows you to select/unselect the facilities to be run in the analysis - "amOnBarrier": informs whether the health facility is located (“yes”) or not (“no”) on a barrier. The analysis cannot be performed if health facilities are located on barriers. If one or several of the health facility(ies) is/are located on a barrier, you can do one of two options:
- "amOnZero": informs whether the health facility is located (“yes”) or not (“no”) on a landcover category that has a speed of zero set in the travel scenario table. In this case the analysis cannot be performed, and you can do one of two options:
- "amOutsideDEM": informs whether the health facility is located (“yes”) or not (“no”) outside of the DEM extent (i.e. outside of the extent of the project). Facilities that are outside the DEM extend cannot be considered in the analysis and their coordinates must be corrected if there are supposed to be within the DEM extent. - "amCatLandCover": provides information on the land cover classcategory, i.e. the pixel value in the land cover raster layer. - "amDemValue": provides information on the DEM, i.e. the pixel value in the DEM raster layer. |
(6) “Type of analysis”: Select the type of analysis you want to conduct: isotropic (ignores the DEM and is slope-independent) or anisotropic (uses the DEM and is slope-dependent). In this exercise, we will select “Anisotropic” under "Type of analysis". This implies that the DEM is used to compute slopes, that are in turn used to modify the speed of travel indicated in the travel scenario table when either the "walking" or "bicycling" travel modes have been chosen for at least one landcover category. Refer to Section 3.3.2 for details on how the slope affects speeds of travel. If the "isotropic" type of analysis is chosen, slopes have no effects and the speeds of travel are not corrected.
(7) “Direction of travel”: Choose the direction of movement considered for the patients, either "From facilities" or "Towards facilities". This choice is only visible when an anisotropic mode has been chosen, because the direction of travel can influence the time of travel. To do the exercise, choose "Towards facilities".
(8) The option to use "knight's move" allows one to perform an analysis on 16 neighbors cells instead of 8. It is slower, but more accurate and tends to give more rounded catchments in area of uniform landcover. We will not use this option for the exercise.
(9) “Maximum travel time (minutes)": Specify the maximum travel time (in minutes) after which the analysis stops. For the exercise, specify 120 minutes. Specify “0” in this field if you want to compute travel time for the full extent of the study area, i.e. with no limit of travel time.
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Starting with version 5.2.4 of AccessMod, travel times are only given in integer numbers of minutes in all output with travel times (raster and tables). This was done to minimize the size of travel time raster files. If you specify "0" for the "maximum travel time", the maximum travel times that can be computed is actually 32'767 minutes (i.e. 22 days, 18 hours and 7 minutes), which should cover the countries in the vast majority of cases. If output travel times exceed this limit, the corresponding cell values in the output travel time raster will be encoded with |
(910) “Add short tags”: Give short tags to be attached to the different outputs of the analysis. We will use "accessibility 120" for the present exercise.
Validation:
(1011) The validation section tells you if everything is fine for you to start the analysis. First it gives you an estimation of the required memory and disk space necessary to run your analysis. Note that these estimations are indicative, and the real requirements may vary. If the memory requirements are close to the memory allocation you gave to the Virtual machine, it is a good idea to increase the latter (see Section 4.2 for how to do that). If anything is wrong in the settings, the "Compute button" will be red and a warning/error message will appear in the list, indicating errors that you will need to address prior to running the analysis. If everything is fine and all the fields have been correctly filled, a green “OK” will appear next to each item in the list and the "Compute button" will be grey (example here above). When this is the case, you can hit the button to launch the analysis.
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. Once this is the case, go back to the Data module to check the four two output data sets that have been generated:
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- scenario processed class: Table containing the travel scenario that has been processed.
- travel time class: Raster format layer containing the spatial distribution of the travel time to the nearest facility, expressed in minutes.
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Before being able to open and look at these datasets you need to archive and export them outside AccessMod (i.e. outside the AccessMod virtual machine). To do that, do the following steps in the "Data" module:
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The .img file exported by AccessMod might need to be converted into a raster format grid before you can use it to perform other types of analysis in the GIS software you are using. Please refer to the user manual of the GIS software in question to find out how to perform such a conversion. This layer can be used in the zonal statistics tool to measure accessibility coverage at the zone level. Please see Section 5.5.6 for more information. |
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