Consider including the UTM zone definition within the functions

[cforgaci]

This is an issue raised as part of ropensci/software-review#718

• As far as I can tell, you need to work in a projected CRS to perform all spatial operations correctly, and UTM is a good choice. Why not include the UTM zone definition within the functions and let the package determine the UTM zone from the bounding box, rather than the user? What I mean is, consider having an API like this:

get_osm_city_boundary <- function(bb, city_name, multiple = FALSE,
                                  force_download = FALSE) {
  # Check input
  checkmate::assert_character(city_name, len = 1)
  crs <- get_utm_zone(bb) # <-- Here
  checkmate::assert_logical(multiple, len = 1)
  
}

[cforgaci]

This is handled by define_aoi()