def get_features(geojson):
    """
    Helper function to extract features
    from dictionary. If it doesn't find
    it, raise a value error with a more
    informative error message.
    """
    try:
        features = geojson['features']
    except KeyError:
        raise KeyError(
            f'{geojson} is an invalid GeoJSON. Not a feature collection')
    return features
