Work out nearest possible site to lat & lon coordinates
        and return observation data for it.
        
        lat:    float or int.  Latitude.
        lon:    float or int.  Longitude.

def nearest_loc_obs(self, lat, lon):
        """
        Work out nearest possible site to lat & lon coordinates
        and return observation data for it.
        
        lat:    float or int.  Latitude.
        lon:    float or int.  Longitude.
        """
        sitelist = self.loc_observations(SITELIST)
        sites = parse_sitelist(sitelist)
        site = get_nearest_site(sites, lat, lon)
        return self.loc_observations(site)