Join geojsons into one. The spatial reference system of the output file is the same
        as the one of the last file in the list.

    Args:
        input_files (list): List of file name strings.
        output_file (str): Output file name.

def join(input_files, output_file):
    '''
    Join geojsons into one. The spatial reference system of the output file is the same
        as the one of the last file in the list.

    Args:
        input_files (list): List of file name strings.
        output_file (str): Output file name.
    '''

    # get feature collections
    final_features = []
    for file in input_files:
        with open(file) as f:
            feat_collection = geojson.load(f)
            final_features += feat_collection['features']

    feat_collection['features'] = final_features

    # write to output file
    with open(output_file, 'w') as f:
        geojson.dump(feat_collection, f)