city-distance

Research

Calculate line-of-sight and road distances between two cities using free OpenStreetMap services.

QUICK START

How to use this skill

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Source SKILL.md: https://github.com/besoeasy/open-skills/blob/HEAD/skills/city-distance/SKILL.md

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City Distance Skill

Purpose: Calculate line-of-sight and road distances between two cities using free, API-keyless public services and local haversine calculations.

What it does:

Computes line-of-sight distance using the Haversine formula.
Uses OpenStreetMap routing endpoint (routing.openstreetmap.de) to compute road distance without an API key.
Optionally lists intermediate cities by sampling points along the route and reverse-geocoding with Nominatim (free) to find nearby settlements.

Files:

city_distance_calculator.js — example Node.js script demonstrating the calculations.
examples: EXAMPLES.md with worked examples (Paris–Berlin, Paris–Dubai)

When to use:

Quickly get straight-line and driving distances between two cities without paying for an API.
Generate a rough list of settlements along a driving route for planning or visualization.

Prerequisites:

Node.js 18+ for the Node.js examples (native fetch available)
curl and jq for Bash examples

Agent prompt:

Calculate both the straight-line (Haversine) distance and the driving distance between {cityA} and {cityB} using free OpenStreetMap services. Return distances in km and optionally list major towns along the driving route.

Examples

Bash (uses OSM routing, jq):

set -euo pipefail
CITY_A_LAT=48.8566
CITY_A_LON=2.3522
CITY_B_LAT=52.52
CITY_B_LON=13.4050

URL="https://routing.openstreetmap.de/routed-car/route/v1/driving/${CITY_A_LON},${CITY_A_LAT};${CITY_B_LON},${CITY_B_LAT}?overview=false"

curl -fsS --max-time 10 "$URL" | jq -r '.routes[0].distance / 1000'

Node.js (uses native fetch, AbortController, error handling):

// city_distance_calculator.js
async function fetchJson(url, timeoutMs = 10000) {
  const controller = new AbortController();
  const id = setTimeout(() => controller.abort(), timeoutMs);
  try {
    const res = await fetch(url, { signal: controller.signal });
    clearTimeout(id);
    if (!res.ok) throw new Error(`HTTP ${res.status}`);
    return await res.json();
  } catch (err) {
    clearTimeout(id);
    throw err;
  }
}

function haversine(lat1, lon1, lat2, lon2) {
  const R = 6371e3;
  const toRad = d => (d * Math.PI) / 180;
  const φ1 = toRad(lat1), φ2 = toRad(lat2);
  const Δφ = toRad(lat2 - lat1), Δλ = toRad(lon2 - lon1);
  const a = Math.sin(Δφ/2)**2 + Math.cos(φ1)*Math.cos(φ2)*Math.sin(Δλ/2)**2;
  const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
  return (R * c) / 1000;
}

(async () => {
  const paris = { lat: 48.8566, lon: 2.3522 };
  const berlin = { lat: 52.52, lon: 13.4050 };
  console.log('Line-of-sight (km):', haversine(paris.lat, paris.lon, berlin.lat, berlin.lon).toFixed(2));

  const url = `https://routing.openstreetmap.de/routed-car/route/v1/driving/${paris.lon},${paris.lat};${berlin.lon},${berlin.lat}?overview=false`;
  const data = await fetchJson(url, 15000);
  console.log('Driving distance (km):', (data.routes[0].distance / 1000).toFixed(2));
})();

Notes / Rate limits:

routing.openstreetmap.de and Nominatim are public services and have usage policies and rate limits. Use respectfully (cache results, avoid heavy automated polling).
For production-grade use, consider hosting your own OSRM/GraphHopper instance or using a commercial API with SLA.