Add UI-09: monochrome dark map tiles
Today's OSM tiles are the default tan/cream basemap, which looks nothing like the mockups regardless of HUD styling. Recommends switching to CARTO's free Dark Matter raster tiles over a client-side color filter on OSM tiles, since the mockups depend on the map itself being dark, not just tinted. Flags a real interaction with V3-11's offline tile cache: it's keyed by (z,x,y) with no provider tag, so switching tile sources without a cache-busting step would silently serve stale OSM tiles under CARTO's URL. That's folded into this ticket's implementation, not left as a followup bug.
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# UI-09 — Monochrome dark map tiles
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**Depends on** nothing · **Size** S · **Status** Not started
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## Goal
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Replace the tan/cream default OpenStreetMap raster style with a monochrome dark map, so
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the map actually looks like it belongs in a dark-mode HUD instead of a light basemap
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punched through a dark overlay.
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## Context
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`RideMap`, the Plan/Route Planning canvas, and every Stitch mockup all assume a dark or
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near-monochrome map underneath the HUD. Today's `TileLayer` (`ride_map.dart`) points at
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`tile.openstreetmap.org`, OSM's standard light/tan default style — the actual on-device
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result is nothing like the mockups, regardless of how dark the chrome on top of it is.
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This affects every screen that shows a map (Map HUD, Plan, Route Planning, and UI-01's
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dimmed background on every other tab), so it's worth settling once, early, rather than
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each screen ticket discovering the same mismatch independently.
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## Design
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Two real options, not one obvious answer:
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**Option A — switch tile provider to CARTO's "Dark Matter" basemap.**
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`https://{s}.basemaps.cartocdn.com/dark_all/{z}/{x}/{y}{r}.png` (subdomains a-d, retina
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`{r}` variant available, max native zoom 20). Purpose-built dark, desaturated/monochrome
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cartography — closest to the mockups with the least engineering. Free for reasonable
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usage same as OSM's own tiles, but it's a **different third party with its own usage
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policy and attribution requirement** ("© OpenStreetMap contributors © CARTO", not just
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OSM's own attribution) — a real dependency to add, not a style tweak.
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**Option B — keep OSM tiles, apply a color filter client-side.** Wrap `TileLayer` in a
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`ColorFiltered` widget using a `ColorFilter.matrix` that desaturates and inverts/darkens
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the tan basemap into a monochrome dark look. No new third party, no new attribution, and
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V3-11's offline tile cache keeps working against the exact tiles it already knows about
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— but the result is a filtered light map, not tiles actually designed for dark
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presentation, and will read as slightly "off" next to CARTO's purpose-built version
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(road/building contrast tuned for light backgrounds doesn't always invert cleanly).
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**Recommendation: Option A.** The mockups' whole aesthetic depends on the map itself
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being dark, not just tinted dark, and CARTO's dark tiles are a well-established, free,
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no-API-key option already widely used in the Flutter/Leaflet ecosystem for exactly this.
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The added attribution line and a second host to trust are a small, one-time cost.
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**V3-11 interaction:** the offline tile cache (`FileTileCache`/`CachedTileProvider`) is
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already keyed by `TileKey(z, x, y)` with no provider-specific data baked in — but that
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means a cache built against OSM tiles and a cache built against CARTO tiles are
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**indistinguishable to the cache** despite being visually different. Switching providers
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without a plan here would silently serve stale, wrong-looking cached OSM tiles once
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CARTO's URL is live. This needs a cache-busting or provider-tagging fix as part of this
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ticket, not a separate one — see Implementation.
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## Implementation
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1. Add a `provider`-qualified cache key (or a cache-version bump that invalidates
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existing V3-11 cache contents wholesale) so switching tile sources can't silently
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mix cached tiles from two visually different sources.
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2. Update `RideMap`'s `TileLayer` (and the Route Planner's separate `TileLayer` instance
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— see `route_planner_screen.dart`) to CARTO's dark tile URL template, correct
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`subdomains`, and `maxNativeZoom: 20`.
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3. Update the attribution requirement — check whether `flutter_map`'s
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`RichAttributionWidget`/`AttributionWidget` is in use anywhere already, or add one;
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OSM-only attribution is no longer sufficient once CARTO tiles are in the mix.
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4. Update `tileUserAgent`/any OSM-specific comments in `ride_map.dart` that assumed OSM's
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tile servers specifically (the "respect OSM's usage policy" reasoning still applies in
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spirit to CARTO's own policy, but the specific server being addressed changes).
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5. Re-verify V3-11's tile math/download flow still works end-to-end against the new URL
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template (tile enumeration and caching are provider-agnostic already; only the fetch
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URL construction needs updating).
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## Acceptance criteria
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- [ ] The map renders in a dark, desaturated/monochrome style matching the Stitch
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mockups, not OSM's default tan basemap
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- [ ] Correct attribution for both OpenStreetMap and CARTO is shown wherever the map is
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shown
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- [ ] Switching tile providers does not silently serve stale, visually-mismatched
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cached tiles from before the switch (V3-11's cache is invalidated or
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provider-tagged)
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- [ ] Both `RideMap` and the Route Planner's independent `TileLayer` are updated
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consistently — one dark style everywhere, not just on the screens that happened to
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get touched first
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## Tests
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- Existing `ride_map`/route-planner widget tests updated for the new tile URL and still
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passing
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- Unit: cache-key/versioning change is exercised the same way V3-11's eviction tests
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are — a cache built under the old scheme does not get served for the new provider
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## Risks
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- **A second third-party tile host is a real dependency, not a free color swap** — its
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own usage policy, its own risk of being blocked if misused, and its own attribution
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obligation. Treat it with the same care V3-11 already applies to OSM (rate-limit
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respecting, no bulk prefetch, real user agent).
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- If CARTO's free tier ever proves insufficient or is discontinued, Option B (a color
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filter over OSM tiles) is the fallback with no new third-party dependency — worth
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keeping in mind as a documented Plan B, not re-deriving from scratch later.
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## Out of scope
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A fully custom/self-hosted vector tile style — much larger scope, and not needed to hit
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"looks like the mockups" today.
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