# Method — DC transit lunch context

The 20 rows are original joins of three official public layers: 113 WMATA/DC GIS entrance and elevator point records, 252 DC DPR property polygons, and 12 historical DC DDOT vending geometries. Fresh retrievals on 24 October 2026 matched the saved input semantics. The catalogue dates are 20 March 2024, 12 September 2025 and 30 January 2023 respectively. Vending metadata explicitly states accuracy as of **1 April 2014**.

## Calculation

`harness/transit-lunch-context/build.py` ran twice on identical packaged snapshots using Python's standard library. Both output files were byte-identical. Source, runner and output hashes plus exact execution timestamps are recorded in `review/evidence/transit-lunch-context/run-record.json`.

Group entrance/elevator records by normalized station name. Preserve SW in Federal Center SW; collapse only the explicit Judiciary Square NE/SW elevator aliases and the documented Mt Vernon spelling variation. For each station, compare every published entrance with every historical vending geometry and select the closest pair by Haversine distance. Break ties by entrance GIS ID and vending object ID. Select the DPR geometry whose representative is closest to that entrance; break ties by object ID. Retain all joined feature IDs and unrounded values.

Point representatives use their published coordinate. Polygon/line representatives use the arithmetic mean of every stored vertex, including repeated closing vertices. This is deliberately the saved prototype method: **not a geometric centroid, boundary distance, public entrance, walking route or shortest path**. Earth radius is 6,371,008.8 metres. Display distances round to integer metres. The 20-station sample sorts by that rounded vending-representative distance and station name; it is not a lunch, safety or accessibility ranking.

## Identity correction and limits

The prior prototype accidentally split Federal Center SW into two stations by removing SW from its elevator label. This run merges its two feature records and fills the twentieth place using the next station under the same selection rule. The earlier snapshot remains outside this edition; the comparison manifest records its hash and the change.

Entrance count means published feature records, including elevators; it is not a verified number of distinct or open doors. DPR properties are not all public parks and their representative coordinates are not entry points. Null amenity fields remain unknown. A published active flag does not establish operating hours or accessible routes. All walking_route_metres are null; no pedestrian graph, OpenStreetMap input, current elevator condition or physical inspection was used. Historical vending capacity and geometry do not establish a current truck event, availability or legal permission.

## Attribution and reuse

Each of the three official catalogue records declares CC BY 4.0. Attribute WMATA/DC GIS, DC Department of Parks and Recreation and District Department of Transportation, identify this compilation and its normalization/calculations, and retain the source dates and uncertainty. Original compilation data: CC BY 4.0. Original runner: MIT. Website text is not redistributed as dataset input. Source-ledger hashes identify the opened material. CSV is a separate rendering of the canonical JSON rows.