...
There are two correction modes available (since version 5.6.25):
- "Population value known": for this, it is assumed the attribute table of the administrative unit shapefile has a column informing about the official number of population in each administrative unit. AccessMod will therefore ensure, in each administrative unit, that the population redistributed outside barriers sum up to the official population number of that unit.
- "Population value not known": for this, it is assumed you do not know the official total distribution of each administrative unit. AccessMod therefore assumes that the sum of population in each administrative unit is the correct one and redistribute this total population outside barriers.
...
- Population distribution raster;
- The land cover merge raster;
- The shapefile of the Administrative boundaries down to the sub-national level (with an attribute column holding the official population number, if needed).
The steps that are automatically applied by the tool to correct the population are the following ones:
- The population distribution grid (“total population“) is first masked with the landcover merge grid in order to extract the population outside of the barriers, which gives a “partial population” grid, whose sum of pixels values gives the “partial population”.
- The ratio between total and partial population is computed.
- The “partial population” grid is multiplied by this ratio. This process produces a “corrected population“ grid that has no population in barrier pixels, but whose sum of population is equal to the sum of population of the original population distribution grid. If the correction mode "Population value known" was chosen, an additional factor is applied to ensure that the sum of population now matches the population value found in the attribute table.
These three steps are done for each administrative unit found in the input administrative boundaries shapefile. It is therefore recommended to use administrative level 3 or 4 (rather than 1 or 2) so that the population on barriers will be redistributed close to the barriers within a small administrative unit.
...