# V3-11 — Offline tile pre-download

**Phase** Ride management · **Depends on** V3-04 · **Size** M · **Status** Not started

## Goal
Have map tiles available where there is no signal.

## Context
`flutter_map` caches what it renders, so a re-viewed ride works. A **mountain ride with no
signal shows blank tiles** — precisely where a map is most wanted.

## Design
**Respect OSM's tile usage policy. Bulk prefetching their public servers is prohibited**
and would get the app blocked. This constraint decides the design:

- Pre-download only a **user-chosen area**, at a **limited zoom range**, with a visible
  tile count and size estimate before starting
- Rate-limited, sequential, cancellable
- If this becomes a headline feature, move to a paid tile provider or self-hosted tiles.
  Do not scale it on OSM's donated infrastructure.

Natural pairing with V3-07: pre-download the corridor along a planned route rather than a
rectangle — far fewer tiles for the same usefulness.

## Implementation
1. Persistent tile cache with a size cap and eviction (`flutter_map_cache` or similar)
2. Area selection on the map, plus a "download along this route" option
3. Tile count and MB estimate **before** any request
4. Sequential fetch with a delay, a progress indicator and cancellation
5. Settings: cache size, and a way to clear it

## Acceptance criteria
- [ ] A downloaded area renders with the network off
- [ ] Count and size shown before download starts
- [ ] Cancellable mid-download, keeping what has already arrived
- [ ] A hard cap on tiles per request — no unbounded area selection
- [ ] Cache size visible and clearable

## Tests
- Tile-count maths for a bounding box across zoom levels
- Cache eviction at the cap
- Cancellation leaves a consistent cache
- **Manual:** aeroplane mode over a downloaded area

## Risks
- **Abusing OSM's servers.** Cap, rate-limit, and be conservative. A blocked user agent
  would break the map for everyone.
- Storage growth. Tiles add up fast; the cap is not optional.

## Out of scope
Vector tiles or a full offline basemap.