Low-Pollution Routing App Build

Project: Air Pollution Route Finder App — Full Stack (iOS, Android, Web + Backend)

I need a production-ready app that finds the lowest-pollution route between two points in London.

What it does:
- User enters A to B, app returns 3 route options: cleanest, fastest, balanced
- Live air pollution heatmap overlay on the map - street level
- Walking, cycling and driving modes
- Turn-by-turn navigation on mobile
-uses breathme london api, tomtom api


**Required stack:**
- Backend: FastAPI or Node.js
- Mobile: React Native, Type script
- Web: React + TypeScript + MapLibre GL JS

Hard requirement: Pollution scores must be pre-cached per road segment — not calculated per request. Tell me exactly how you'll achieve this in your proposal.