Measure Country's Distance from the Equator using a Shapefile-CodePudding

I want to measure the distance of countries position relative to the equator, and I got the idea to do this using a shape-file with R. I do not know how feasible this is, or whether it is possible at all, but I do know that it is possible to measure distance.

Using the shape-files from the

Next the measurement of distance between country and equator line. Ideally, the calculation would yield a panel data with country and distance.

Would this be possible?

CodePudding user response：

Let us obtain a world map shapefile using the rnaturalearth package:

library(sf)
library(rnaturalearth)
library(tidyverse)

map_world <- ne_countries(returnclass = 'sf')

To simplify the example, let's choose a few different countries:

countries <- c("United States of America",
               "United Kingdom",
               "Australia",
               "Argentina",
               "Chad")

Now we filter out these countries and find their centroids. We then generate an extra sfc column that is the projection of the centroids onto the equator. Finally, we measure the distance between the centroids and the equator points:

country_points <- map_world %>% 
  filter(admin %in% countries) %>% 
  st_centroid() %>%
  bind_cols(st_coordinates(.)) %>%
  select(admin, X, Y) %>%
  rowwise() %>%
  mutate(equator = st_sfc(lapply(X, function(x) st_point(c(x, 0))),
                          crs = st_crs(map_world))) %>%
  mutate(distance_equator = st_distance(geometry, equator)[,1]) %>%
  select(-equator)

This results in the distance measurements of all the countries' centroids from the equator:

country_points
#> Simple feature collection with 5 features and 4 fields
#> Geometry type: POINT
#> Dimension:     XY
#> Bounding box:  xmin: -103.5729 ymin: -34.73683 xmax: 134.3143 ymax: 53.8083
#> CRS:            proj=longlat  datum=WGS84  no_defs  ellps=WGS84  towgs84=0,0,0
#> # A tibble: 5 x 5
#> # Rowwise: 
#>   admin                          X     Y              geometry distance_equator
#>   <chr>                      <dbl> <dbl>           <POINT [°]>              [m]
#> 1 Argentina                 -64.8  -34.7 (-64.75442 -34.73683)         3862566.
#> 2 Australia                 134.   -25.8   (134.3143 -25.7631)         2864730.
#> 3 United Kingdom             -2.76  53.8   (-2.759269 53.8083)         5983219.
#> 4 Chad                       18.6   15.3   (18.57333 15.27628)         1698647.
#> 5 United States of America -104.    44.8  (-103.5729 44.75598)         4976646.

Furthermore, we can plot the result like this:

ggplot(data = map_world)  
  geom_sf()  
  geom_hline(yintercept = 0, color = 'red', size = 1)  
  geom_segment(data = country_points, size = 1,
               aes(X, Y, xend = X, yend = 0), color = 'red')

^{Created on 2022-10-27 with reprex v2.0.2}