Distances to the Storting

nor_distance.R

library(sp)
library(raster)
library(viridis)
library(rgdal)
library(rnaturalearth)


### need two things, presumably
###  - a polygon mask
###  - a population raster
###
### Could in theory use a digital elevation map to get "low cost" routines not over mountains.

### (1) Get the polygon in to clip/extract later
nor_poly <- ne_countries(scale = "medium", country = "Norway")

### (2) Get the raster in
### Raster from WorldPop
infile <- "nor_ppp_2020_constrained.tif"
GDALinfo(infile)
nor <- raster(infile)

### Replace missing values with zero values
nor <- calc(nor, fun = function(x) {
    replace(x, !is.finite(x), 0)
})

### Extract the portions in the polygon
nor <- raster::mask(nor, nor_poly)

### Get the location of the Norwegian Parliament
### Not actually, more https://latitude.to/map/no/norway/cities/oslo
storting <- data.frame(x = 10.74609, y = 59.91273)

### Update with storting info as field value 999
nor <- rasterize(storting, nor, field = 999, update=TRUE)

### Calculate distance to field 999, omitting areas not in polygon
### This might take ten minutes or so
d <- gridDistance(nor, origin = 999, omit=NA)

### We'd want to multiply the distances by the count of people and
### then divide by the sum of the count to get the population-weighted
### average distance
norvals <- getValues(nor)
d2 <- getValues(d)
nor_avg <- sum(norvals * d2, na.rm = TRUE) / sum(norvals, na.rm = TRUE)

### Would this be in metres? proj is longlat, so yes