This is a string (or a character vector) that contains the
OS grid Reference.
coord_system
By default, this is "BNG" which stands for British
National Grids. The other option is to set coord_system = "WGS84", which
returns latitude/longitude coordinates (more info can be found here
https://www.epsg-registry.org/).
Value
vector made of two elements: the easting and northing (by default) or
latitude and longitude coordinates.