def _validate(self):
        """ Enforce some structure to the config file """
        # This could be done with a default config

        # Check that specific keys exist
        sections = odict([
                ('catalog',['dirname','basename',
                            'lon_field','lat_field','objid_field',
                            'mag_1_band', 'mag_1_field', 'mag_err_1_field',
                            'mag_2_band', 'mag_2_field', 'mag_err_2_field',
                            ]),
                ('mask',[]),
                ('coords',['nside_catalog','nside_mask','nside_likelihood',
                           'nside_pixel','roi_radius','roi_radius_annulus',
                           'roi_radius_interior','coordsys',
                           ]),
                ('likelihood',[]),
                ('output',[]),
                ('batch',[]),
                ])  

        keys = np.array(list(sections.keys()))
        found = np.in1d(keys,list(self.keys()))

        if not np.all(found):
            msg = 'Missing sections: '+str(keys[~found])
            raise Exception(msg)

        for section,keys in sections.items():
            keys = np.array(keys)
            found = np.in1d(keys,list(self[section].keys()))
            if not np.all(found):
                msg = 'Missing keys in %s: '%(section)+str(keys[~found])
                raise Exception(msg)