select_borders.py

#!/usr/bin/env python3
import gzip
import json
import os

from shapely.geometry import mapping, shape

# File for admin data outputed by Cosmogony
COSMOGONY_DATA = 'admins.json.gz'

# Directory where to put output json
OUTPUT_DIR = 'output'

# Target admins to include in the output
TARGETS = {
    'paris': {
        'filter': {'admin_level': 4, 'name': 'Île-de-France'},
    },
    'lyon': {
        'filter': {'admin_level': 6, 'name': 'Métropole de Lyon'},
    }
}

if not os.path.exists(OUTPUT_DIR):
    os.mkdir(OUTPUT_DIR)

def match(admin_data):
    for name, meta in TARGETS.items():
        if all(admin_data[key] == val for key, val in meta['filter'].items()):
            return name

    return None

with gzip.open(COSMOGONY_DATA) as f:
    for data in map(json.loads, f):
        matching_target = match(data)

        if matching_target:
            print("Found", matching_target)
            geometry = shape(data['geometry'])
            output_path = os.path.join(OUTPUT_DIR, matching_target + ".json")

            with open(output_path, 'w') as f:
                f.write(
                    json.dumps(
                        mapping(geometry.simplify(0.01)),
                        indent=4
                    )
                )