What do we actually know about this place, how current is that knowledge, and where do I check today before entering the water?
Swimmable Cities may present official historical assessments and clearly labelled seeded context, but it must never dress a seasonal baseline as a live safety status. Source, data age, official-versus-seeded provenance, and the path to the current local notice must remain part of the primary interaction.
Case-study thesis
What the finished product should prove.
This is the behavior to build toward. The implementation receipts below remain the record of what exists today.
The interaction is a trust handoff from a map to evidence. The most important state is often not good or bad, but old, unknown, seeded, or check today elsewhere.
State model
The interface has to make these states real.
If two states would look identical to the person, the implementation is not finished.
01
Nearby places
Managed swim places can be found even if map tiles, geolocation, or rich media fail.
02
Official baseline
A sourced classification is shown with season, date, jurisdiction, and history.
03
Seeded context
A prototype or manually seeded place is visibly different from an official assessment.
04
Source detail
The person can open the agency, measurement basis, classification history, and data age.
05
Current notice available
The interface provides the authoritative local path for today without paraphrasing it into its own safety claim.
06
Current notice unavailable
The absence of a live local notice is explicit and does not fall back to the seasonal baseline as if it were current.
07
Out of season or stale
Old assessments remain useful context but are visually downgraded as current decision support.
08
Map unavailable
The place list and evidence remain accessible when tile services or tokens fail.
Edge cases
The boring failures are part of the product.
A user checks the spot outside the official bathing season
Heavy rain or another local event may make the seasonal baseline less relevant
The current local notice cannot be reached
Two agencies publish conflicting or differently dated information
A seeded place later gains an official source
Geolocation is denied
Mapbox or another tile provider is unavailable
Definition of done
The future case study needs these receipts.
Every official classification exposes source, season, date, and jurisdiction on the primary spot flow
Seeded places cannot visually or semantically masquerade as official assessments
The interface never turns a seasonal baseline into the statement safe to swim today
If a current notice is unavailable, that absence is a first-class state rather than a hidden broken link
The place list and source information remain usable without map tiles or geolocation
Estonia and Finland spots carry EEA classifications under the Bathing Water Directive.
indicators
E. coli
Official assessments use E. coli and intestinal enterococci. History stays on the spot.
Taiwan
Seeded
Taiwan spots are labelled as seeded. The app does not invent official grades for them.
non-advisory
Copy
Tests forbid “safe to swim today.” Check the official local notice before you enter the water.
The job
A spot card you can read at the water’s edge.
Official bathing-water portals are authoritative and hard to use when you are already standing at the railing. I wanted a spot card with data age, an official grade or a seeded label, nearby context, and a city action brief.
At the water
Find the place. Read the baseline. Check today’s notice.
01
Find a managed place
The map is first. Closest spots, city, country, and a season label sit on the card before any promise about today.
02
Read official or seeded
EU spots must carry an officialAssessment. Taiwan spots must be seeded. The UI keeps those labels distinct.
03
Open sources
The sources panel cites the European Environment Agency and the Swimmable Cities movement workstreams. Data age stays visible.
04
Check the local notice
Copy tests keep the app from saying it is safe to swim today. The last step is still the city’s own notice.
Design decisions
Decisions.
01
Data contract
Official and seeded cannot share a costume.
If an Estonia or Finland spot is on the map, it has an official assessment. If a Taiwan spot is on the map, it is seeded and labelled. Tests enforce the split so a later edit cannot blur it.
02
Language
The caveat is part of the product.
I did not want a sources footnote that a hurried reader could miss. Copy tests and the sources panel keep the non-advisory sentence in the interface.
03
Map
The places exist even when tiles do not.
A missing Mapbox token should not erase the spots. The prototype renders without tiles; interactivity waits on a public pk. token.
The working stack
Built with.
Data
swimData.ts
EEA 2025 classifications for Estonia and Finland. Seeded Taiwan. Tests for the split.
Copy
Non-advisory contract
copy.test.ts and SourcesPanel. The UI must not say safe to swim today.
Map
Mapbox
Tiles only. Token in .env. Prototype works without it.
Host
swim.haam.co
Vercel Vite/React map prototype. Movement name: Swimmable Cities.
In evidence
Evidence.
01Official EU 2025 baselines on Estonia and Finland spots
02Taiwan spots labelled as seeded
03A sources caveat that tests will fail if it disappears
04A map that still lists places when tiles are missing
Where it stops
The baseline is last season. Today is still the city’s.
There is no live sample engine and no rain-triggered CSO in this pass. Mapbox tiles on the public host need a token. Native swim logic is deferred.
Do not say safe to swim today. Do not call it a live water-quality product. Accessibility audit not recorded.
HAAM’s role
I kept the official baseline, and I kept today in the city’s hands.
Baseline versus today, seeded versus official labels, city action brief, Mapbox prototype, EEA 2025 data, and copy tests. Direct work, 2026.
