docs: def import_basemap():
      """
      Try to import Basemap and print out a useful help message
      if Basemap is either not installed or is missing required
      environment variables.
  
      Returns
      ---------
      has_basemap : bool
      Basemap : Basemap package if possible else None
      """
  
      Basemap = None
      has_basemap = True
      has_cartopy = import_cartopy()[0]
      try:
          from mpl_toolkits.basemap import Basemap
          WARNINGS['has_basemap'] = True
      except ImportError:
          has_basemap = False
          # if they have installed cartopy, no warning is needed
          if has_cartopy:
              return has_basemap, False
          # if they haven't installed Basemap or cartopy, they need to be warned
          if not WARNINGS['basemap']:
              print(
                  "-W- You haven't installed a module for plotting maps (cartopy or Basemap)")
              print("    Recommended: install cartopy.  With conda:")
              print("    conda install cartopy")
              print(
                  "    For more information, see http://earthref.org/PmagPy/Cookbook#getting_python")
      except (KeyError, FileNotFoundError):
          has_basemap = False
          # if cartopy is installed, no warning is needed
          if has_cartopy:
              return has_basemap, False
          if not WARNINGS['basemap']:
              print('-W- Basemap is installed but could not be imported.')
              print('    You are probably missing a required environment variable')
              print(
                  '    If you need to use Basemap, you will need to run this program or notebook in a conda env.')
              print('    For more on how to create a conda env, see: https://conda.io/docs/user-guide/tasks/manage-environments.html')
              print(
                  '    Recommended alternative: install cartopy for plotting maps.  With conda:')
              print('    conda install cartopy')
      if has_basemap and not has_cartopy:
          print("-W- You have installed Basemap but not cartopy.")
          print("    In the future, Basemap will no longer be supported.")
          print("    To continue to make maps, install using conda:")
          print('    conda install cartopy')
  
      WARNINGS['basemap'] = True
      return has_basemap, Basemap