sp::bbox object as
input and returns a single raster object covering that extent. You should have
an api_key from Mapzen.
get_mapzen_terrain(bbx, z, prj, api_key = NULL, expand = NULL, ...)sp::bbox object that is used to select x,y,z tiles..Renviron file with the variable "mapzen_key"config=timeout(x) where x is a numeric value in
seconds. Multiple configuration functions may be passed as a
vector.