Philippine GIS & GeoJSON Integration Guide

2. mapaPH RFC 7946 GeoJSON Feature Schema

Boundary GeoJSON files exported from mapaPH tools comply with the Internet Engineering Task Force (IETF) RFC 7946 standard. Every administrative polygon contains standard properties aligned with the Philippine Standard Geographic Code (PSGC) published quarterly by the Philippine Statistics Authority (PSA).

{
  "type": "FeatureCollection",
  "name": "philippine_municipalities_2024",
  "crs": {
    "type": "name",
    "properties": { "name": "urn:ogc:def:crs:OGC:1.3:CRS84" }
  },
  "features": [
    {
      "type": "Feature",
      "id": "037114000",
      "properties": {
        "psgc": "037114000",
        "psgc10": "0307114000",
        "name": "Subic",
        "level": "Municipality",
        "province": "Zambales",
        "provincePsgc": "037100000",
        "region": "Central Luzon",
        "regionCode": "03",
        "incomeClass": "1st",
        "population2020": 111912,
        "landAreaSqKm": 287.16
      },
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [120.2312, 14.8814],
            [120.2451, 14.8923],
            [120.2684, 14.8752],
            [120.2312, 14.8814]
          ]
        ]
      }
    }
  ]
}

RFC 7946 Compliance Rules

• Axis order: Coordinates are always stored as [longitude, latitude, elevation]. Longitude ranges from 116.0° E to 127.0° E; latitude ranges from 4.5° N to 21.5° N.
• Winding order (Right-hand rule): Exterior polygon boundary rings run counter-clockwise. Interior boundary rings representing land enclaves or water bodies run clockwise.
• Coordinate decimal precision: Six decimal places (0.000001°) provides approximately 0.11 meters (11 centimeters) ground precision at Philippine latitudes. Exporting beyond six decimal places increases JSON payload size without adding genuine surveying resolution.
• Archipelagic MultiPolygons: Philippine coastal provinces and island municipalities (such as Palawan, Romblon, Batanes, and Sulu) must use MultiPolygon geometries to avoid self-intersecting lines between discrete islands.

3. Client-Side Spatial Queries with Turf.js

To identify which Philippine province, city, or municipality contains a GPS position recorded from a delivery vehicle, mobile application, or field sensor, execute point-in-polygon queries client-side using Turf.js.

import * as turf from '@turf/turf';

// Point coordinate: Kilometer Zero (KM 0), Luneta Park, Manila
// Turf expects coordinates as [longitude, latitude]
const sensorPoint = turf.point([120.9787, 14.5826]);

/**
 * Identifies the administrative unit containing the coordinate.
 * Bounding-box pre-filtering runs first to skip distant polygons in O(1) time.
 */
export function findContainingBoundary(point, featureCollection) {
  const ptCoord = point.geometry.coordinates;

  for (const feature of featureCollection.features) {
    // 1. Fast bounding-box pre-check
    const bbox = turf.bbox(feature);
    if (
      ptCoord[0] < bbox[0] || ptCoord[0] > bbox[2] ||
      ptCoord[1] < bbox[1] || ptCoord[1] > bbox[3]
    ) {
      continue;
    }

    // 2. Exact ray-casting point-in-polygon test
    if (turf.booleanPointInPolygon(point, feature)) {
      return {
        psgc: feature.properties.psgc,
        name: feature.properties.name,
        province: feature.properties.province,
        region: feature.properties.region
      };
    }
  }

  return null;
}

4. TopoJSON Arc-Sharing and Web Optimization

A raw GeoJSON file containing all 1,642 Philippine cities and municipalities with high-resolution coastlines exceeds 45 megabytes. Distributing this volume of JSON over cellular connections causes substantial browser parsing pauses. Converting to TopoJSON reduces transfer size by over 85 percent through topological arc sharing.

Command-Line Conversion with Mapshaper

The open-source Mapshaper CLI tool enables automated simplification while preserving topological adjacency without generating sliver gaps or overlapping polygons:

# 1. Install Mapshaper CLI
npm install -g mapshaper

# 2. Simplify municipal boundaries to 15% detail using Visvalingam weighting
# -clean fixes self-intersections; -filter-islands removes sub-pixel micro-islands
mapshaper ph_municipalities_raw.geojson \
  -clean \
  -simplify dp 15% keep-shapes \
  -filter-islands min-area=50000m2 \
  -o format=topojson precision=0.0001 ph_municipalities_optimized.topojson

5. Reprojecting NAMRIA Shapefiles to WGS 84 via GDAL

When ingesting official cadastral files or land zoning shapefiles from NAMRIA, the DENR Land Management Bureau, or local city planning offices, the input vectors are typically projected in PRS92 Philippine Transverse Mercator (PTM) Zones I through V. Use the Geospatial Data Abstraction Library (GDAL/OGR) to transform these layers into WGS 84 GeoJSON:

# Transform PRS92 Zone III (Metro Manila / Central Luzon, EPSG:3123) to WGS 84 (EPSG:4326)
ogr2ogr -f "GeoJSON" \
  -s_srs "EPSG:3123" \
  -t_srs "EPSG:4326" \
  -lco COORDINATE_PRECISION=6 \
  manila_zoning_wgs84.geojson \
  manila_zoning_prs92.shp