scripts/build-boundary.mjs

// Dissolve the 101 datameet pincode polygons into ONE outer Bengaluru boundary,
// keep only the largest ring (discard small detached pieces), and write it to
// public/ so it can be fetched at runtime by the map and the hex generator.
//
// Run: node scripts/build-boundary.mjs
import { readFileSync, writeFileSync, mkdirSync } from 'fs'
import * as turf from '@turf/turf'

const raw = JSON.parse(
  readFileSync('src/data/bangalore-boundary.geojson', 'utf8'),
)

const polys = raw.features.filter(
  (f) =>
    f.geometry &&
    (f.geometry.type === 'Polygon' || f.geometry.type === 'MultiPolygon'),
)

console.log(`Union of ${polys.length} pincode polygons...`)

// @turf/turf v7's union takes a FeatureCollection of polygons.
let merged = polys[0]
for (let i = 1; i < polys.length; i++) {
  merged = turf.union(turf.featureCollection([merged, polys[i]]))
}

// Keep only the largest polygon ring (discard small detached pieces).
if (merged.geometry.type === 'MultiPolygon') {
  const largest = merged.geometry.coordinates
    .slice()
    .sort((a, b) => turf.area(turf.polygon(b)) - turf.area(turf.polygon(a)))[0]
  merged.geometry = {
    type: 'Polygon',
    coordinates: largest,
  }
}

// Drop holes — keep only the outer ring for a clean single silhouette.
merged.geometry.coordinates = [merged.geometry.coordinates[0]]
merged.properties = { name: 'bangalore-outer-boundary' }

// Smooth out small jagged seams left where the pincode polygons met, without
// distorting the overall city shape. Light tolerance, high quality.
try {
  const simplified = turf.simplify(merged, {
    tolerance: 0.0005,
    highQuality: true,
    mutate: false,
  })
  if (simplified?.geometry?.coordinates?.[0]?.length >= 4) {
    merged = simplified
    merged.properties = { name: 'bangalore-outer-boundary' }
    console.log('Boundary simplified (tolerance 0.0005).')
  }
} catch (err) {
  console.warn('turf.simplify failed, using un-simplified boundary:', err)
}

mkdirSync('public', { recursive: true })
writeFileSync(
  'public/bangalore-outer-boundary.geojson',
  JSON.stringify(merged),
)
// Also write into src/data so it can be statically imported (bundled) by the
// hex generator without a runtime fetch.
writeFileSync(
  'src/data/bangalore-outer-boundary.geojson',
  JSON.stringify(merged),
)
console.log(
  `Outer boundary written (${merged.geometry.coordinates[0].length} vertices).`,
)