A country's neighbours

Which countries border a given country (or countries) – a vectorised lookup built on country_borders().

Usage

neighbors(x, origin = "country.name", scale = "small")

Arguments

x

A vector of country names or codes.

origin

How to read x (default "country.name").

scale

Natural Earth resolution to compute adjacency from. "large" needs the non-CRAN rnaturalearthhires package; see world_geometry().

Value

A tibble with one row per (iso3c, neighbor) pair: the queried country's iso3c, and each bordering country's iso3c and country name (neighbor, neighbor_country). Countries with no land border (islands, e.g. Japan, Madagascar) return zero rows.

Pass a vector, don't loop

Every call rebuilds the whole world's adjacency from polygon topology, so asking about one country costs the same as asking about all of them. x is vectorised, and adding countries to a single call only adds the filtering:

countryatlas::neighbors(c("FRA", "DEU", "ESP"), origin = "iso3c")

Looping instead pays that rebuild once per country – for every bordering country in the world, roughly two orders of magnitude more work than one vectorised call. The same applies to country_borders(), which does the work.

Name clash with igraph

igraph also exports a neighbors(), and it takes a graph and a vertex rather than country names. Whichever package is attached later wins, so if you use both – which country_borders() suggests, for building a graph of the adjacency – qualify this one as countryatlas::neighbors().

Examples

# \donttest{
if (requireNamespace("sf", quietly = TRUE) &&
    requireNamespace("rnaturalearth", quietly = TRUE)) {
  neighbors("France")
  neighbors(c("FRA", "JPN"), origin = "iso3c")   # Japan has no land border
}
#> # A tibble: 8 × 3
#>   iso3c neighbor neighbor_country
#>   <chr> <chr>    <chr>           
#> 1 FRA   SUR      Suriname        
#> 2 FRA   LUX      Luxembourg      
#> 3 FRA   ITA      Italy           
#> 4 FRA   BRA      Brazil          
#> 5 FRA   DEU      Germany         
#> 6 FRA   CHE      Switzerland     
#> 7 FRA   BEL      Belgium         
#> 8 FRA   ESP      Spain           
# }