Methodology & Data Governance | Inventory & Shipping
inventory_shipping_methodology_v2.0 · Last revised 2026-09-26T22:39:11+02:00
Metric Definitions and Methodology
Inventory uses confirmed weekly snapshots for China's main chrome-ore ports; change metrics are calculated from confirmed weekly endpoints.
Main-port inventory covers Tianjin, Lianyungang, Qinzhou/Fangcheng and the unallocated balance for other main ports. Other/unallocated is the calculated balance after subtracting the three named ports. Weekly, 13-week and annual metrics use confirmed, non-null weekly observations only; missing weeks remain null without zero-filling or interpolation. China-wide arrivals and Tianjin lifting have different scopes and are not used to calculate a national inventory balance directly.
AIS and Vessel Verification
The AIS map is a separate vessel-position snapshot. Only samples that pass vessel identity, voyage and destination checks enter the public map.
Vessels are deduplicated by IMO where available; otherwise a normalized combination of vessel name, voyage, origin and expected destination is used. Public samples retain vessel name or IMO, position time, status, origin, destination status and source. Confirmed and monitored destinations are displayed separately, and vessels without a confirmed destination do not enter confirmed arrival or dispatch totals. Positions older than the snapshot validity window are marked expired rather than presented as live AIS. The map shows publicly visible samples and does not represent every vessel in transit.
Forecast Methodology and Error
Seven- and fourteen-day arrivals are model forecasts using arrival history and dispatch pressure; weeks 2-4 publish direction only.
The 7-day forecast blends the latest confirmed arrival with the four-week median. The days 8-14 increment uses the eight-week arrival median adjusted by a capped current dispatch-pressure factor; the 14-day value is cumulative across both windows. Public fields directly provide the 7-day, 14-day, days 8-14 increment, model MAE, naive baseline MAE, relative improvement, sample count and version, so the frontend performs no recalculation. Forecasts exclude unverified vessel arrival schedules and are not confirmed arrivals. The future inventory-direction judgement is suspended while all-main-port lifting coverage is incomplete.
Data Updates and Revisions
Inventory and shipping follow their formal reporting cycles, AIS positions refresh when available, and qualified revisions retain version records.
Inventory updates on formal weekly endpoints. Arrivals, dispatches, afloat cargo, port waiting, unloading and loading update from the same shipping reporting period. AIS position time is a separate snapshot timestamp and never replaces an indicator date. Forecasts are recalculated after a new confirmed report or qualified revision. Late, missing or conflicting data are not silently replaced with zero or stale values; recovery creates a new revision while retaining the superseded version. The page should display indicator date, snapshot time, revision time and revision reason separately.