Clearer default value of window

Analysis/plot_snapshot.py

@@ -30,7 +30,7 @@ from os import path
 
 def snapshot(k, shp_tr_dir, *, dashed = False, light = False,
              new_figure = False, src_crs = ccrs.PlateCarree(),
-             projection = ccrs.PlateCarree(), window = None):
+             projection = ccrs.PlateCarree(), window = False):
     """Plots extrema, outermost contours and max-speed contours.
 
     shp_tr_dir: containing the three shapefiles.