Off-Grid Trails

An offline trail finder for when there's no cell service. Built for the North Georgia mountains and the Smokies.

Download a trail pack on Wi-Fi before you go. After that, everything works in airplane mode:

• Map of nearby trails (OpenStreetMap data, drawn on the phone, no map tiles needed)
• Nearest trail with distance and direction
• "I parked here" car pin and a live arrow back to it
• Breadcrumbs of the path you walked, so you can retrace your steps
• Nearby water, waterfalls, viewpoints, peaks, shelters and trailheads
• Ask Gemma: a small Gemma model runs on the phone with WebLLM (WebGPU). It only answers from the facts in your pack and your GPS. The question buttons also work without the model.

This app is a companion, not a replacement for a paper map, water and telling someone your plan.

Run it locally

Needs Node 22.22.3+ (Node 24 recommended).

npm install
npm run build
npm start            # http://localhost:3000

For live-reload development, run two terminals:

npm run api          # Express API on :3000
npm run dev          # Angular on :4200, proxies /api to :3000

The service worker only runs in the production build (npm run build && npm start).

How it works

Piece	What it does
server.mjs	Express 5. /api/areas, /api/areas/:id/pack, /api/pack-near?lat&lon&r. Queries the Overpass API once, trims the data into a small "pack", caches it 72 hours, rate-limits 20 packs/hour per IP. Serves the Angular build.
areas.mjs	Preset areas (Vogel/Blood Mountain, Amicalola, Laurel Falls, Clingmans Dome, Alum Cave). Add your own bounding boxes here.
src/app/pack-store.ts	IndexedDB: packs, car pin and breadcrumbs live on the phone.
src/app/location.service.ts	GPS (watchPosition) plus a Demo walk that walks a trail so you can test from the couch.
src/app/local-ai.service.ts	WebLLM. Loads gemma3-1b-it-q4f16_1-MLC (~700 MB, one-time), falls back to gemma-2-2b-it-q4f16_1-MLC-1k.
ngsw-config.json	Angular service worker caches the app so it opens with no signal.

GPS works without cell service: the phone talks to satellites, not towers.

Bake the trail packs (do this before deploying)

The public Overpass servers often refuse requests from cloud hosts like Render. So the preset areas are downloaded once on your own computer and shipped with the app:

npm run bake          # writes packs/*.json (takes a minute or two)
git add packs && git commit -m "Bake trail packs"

Re-run it whenever you want fresher trail data. "Pack trails around me" still calls Overpass live, so it may fail on the hosted app; it always works locally.

Deploy to Render

1. Push this folder to a new GitHub repo.
2. In Render: New → Blueprint, pick the repo. render.yaml sets everything up.
3. Open the URL on your iPhone in Safari, then Share → Add to Home Screen.

Optional environment variables: OVERPASS_URLS (comma-separated Overpass endpoints), CACHE_HOURS, PACKS_PER_HOUR, CACHE_DIR.

Test it offline on iPhone

1. On Wi-Fi: open the app, download a pack, tap Download Gemma and wait for "Ready offline".
2. Turn on Airplane Mode (leave Location Services on).
3. Open the app from your Home Screen. Open the pack, tap Use my GPS, drop a car pin, walk around, ask a question.

Gemma needs WebGPU (Safari on iOS 26+). If it isn't available, everything else still works.

Credits

Trail data © OpenStreetMap contributors, ODbL. Packs are fetched through the public Overpass API; please be gentle with it. On-device AI: Gemma via WebLLM.