Get population counts within catchments of sampling sites

This function takes vectors of sampling site longitude and latitude and calculates the total population residing within the drainage catchment of each coordinate pair. Raster data giving population counts per grid cell and a Digital Elevation Model (DEM) are required. By default, the function delineates streams based on the provided DEM. However, an optional shapefile (such as an urban sewer network) can be specified using the path_stream_shp argument and will be used instead of the natural stream network calculated from the DEM. Note that the delineation of catchments along streams (or sewer networks) still depends on the directional flow from the provided DEM. Intermediate spatial variables are written to the directory specified in path_output.

Usage

get_population_catchment(
  lon,
  lat,
  path_pop_raster,
  path_dem_raster,
  path_stream_shp = NULL,
  path_output
)

Arguments

lon

A numeric vector giving the longitudes of the sampling sites in Decimal Degrees.

lat

A numeric vector giving the latitudes of the sampling sites in Decimal Degrees.

path_pop_raster

The file path to a raster object providing population counts in each grid cell. See download_worldpop_data for methods to download population raster data.

path_dem_raster

The file path to a Digital Elevation Model (DEM) raster. See download_elevation_data for methods to download DEM raster data.

path_stream_shp

An optional file path to a stream or sewer network shapefile. If NULL (the default), streams are delineated based on flow accumulation in the provided DEM.

path_output

The file path of an output directory where spatial data will be saved.

Value

A data.frame containing the catchment area and population counts for each sampling site.

Examples

if (FALSE) {

MCO_lon <- c(7.416, 7.434)
MCO_lat <- c(43.734, 43.747)

download_worldpop_data(iso3 = 'MCO',
                       year = 2020,
                       constrained = TRUE,
                       UN_adjusted = FALSE,
                       path_output = tempdir())

download_elevation_data(lon = MCO_lon,
                        lat = MCO_lat,
                        path_output = tempdir())

get_population_catchment(lon = MCO_lon,
                         lat = MCO_lat,
                         path_pop_raster = file.path(tempdir(), 'mco_ppp_2020_constrained.tif'),
                         path_dem_raster = file.path(tempdir(), 'dem.tif'),
                         path_output = tempdir())

}