Finnish postal number geometries download (postinumeroalueet)

postal-code-geometries.ts

/**
 * Convert postal number geometries to WGS84 coordinates for geocoding
 */
import axios from 'axios';
import * as proj4 from 'proj4';
import * as turf from '@turf/turf';
import { promisify } from 'util';
import * as fs from 'fs';

const writeFile = promisify(fs.writeFile);

// Paavo geometry properties
interface Properties {
  readonly objectid: number;
  readonly posti_alue: string;
  readonly vuosi: string;
  readonly nimi: string;
  readonly namn: string;
  readonly kunta: string;
  readonly kuntanro: number;
  readonly pinta_ala: number;
  readonly bbox: [number, number, number, number];
}

// Coordinate definition for EPSG:3067 / TM35FIN. As proj4 does not understand
// urn:ogc:def:crs:EPSG:3067 which would be available in the response crs the
// implementation here is fixed to work with this SRID only, but it is the official
// one in Finland and thus unlikely to change
proj4.defs(
  'TM35FIN',
  '+proj=utm +zone=35 +ellps=GRS80 +towgs84=0,0,0,-0,-0,-0,0 +units=m +no_defs'
);

const endpoint = 'http://geo.stat.fi/geoserver/postialue/wfs';
const params = new URLSearchParams({
  service: 'wfs',
  version: '1.1.0',
  request: 'GetFeature',
  outputFormat: 'json',
  typeName: 'postialue:pno',
  // If need to debug, limit to single postal code
  // featureID: 'pno.1',
});

// Get geometries from Tilastokeskus WFS endpoint
const getGeometries = () => {
  console.log('Download geometries');
  return axios.get(endpoint, { params }).then((result) => result.data);
};

// Process the GeoJSON response and create map to WGS84 centroid coordinate
const calculateCentroids = (
  features: turf.FeatureCollection<turf.Polygon, Properties>
) => {
  console.log('Calculate centroids');

  return features.features
    .map((feature) => ({
      postalCode: feature.properties?.posti_alue,
      // Coordinates from the API are using ETRS-TM35FIN coordinate reference
      // system, and for HubSpot we need WGS84 which is the one used by
      // eg. Google Maps and GPS
      coordinate: proj4(
        'TM35FIN',
        'WGS84',
        turf.centroid(feature).geometry?.coordinates!
      ),
    }));
};

if (!module.parent) {
  getGeometries()
    .then(calculateCentroids)
    .then(() => console.log('Done'))
    .catch((err) => console.error('Failed to execute', err));
}