Journey segmentation model

Canonical unit

Station-to-station section in a given direction, with explicit duration T for every equivalent-level metric. This matches professional survey practice summarised in ../acoustic-survey-methodology.md.

Logical entities (generic railway schema)

City → TransportSystem → Operator?
     → Line → Branch? → Direction
     → Station → Platform?
     → Section (from_station → to_station, direction, topology id)
     → Service / Trip instance (optional)
     → Vehicle / RollingStock (optional)
     → Carriage / position-within-train (optional metadata)

London Underground lines are instances, not hard-coded core types. Tube-specific labels live in a London network profile.

Recording session vs sections

• A session is one continuous recording attempt (may span transfers if user continues — discouraged for v1 clarity).
• Sections are the comparable units after alignment.
• Users may delete/trim segments (e.g. standing mid-tunnel hold) analogous to survey exclusions — exclusions must be flagged.

Alignment outputs

For each section boundary: suggested timestamp, confidence, user-confirmed flag, optional user override reason.

Recommendation

Freeze section-as-unit for public comparison; allow multi-section sessions but require confirmed boundaries before upload.

Confidence: High for unit choice; Medium for automatic boundary accuracy (needs field tests).

Depends on experiment/legal/user-test? Experiments + user tests for alignment UX (tunes-ios).

Links: ../research/06-railway-journey-model.md; ../research/07-journey-alignment.md; ../decisions/ADR-002-generic-railway-schema.md; H16 — Schema.