Strait of Hormuz

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Methodology

What is a "crossing"?

A crossing is recorded when a vessel transits between the west approach zone (Persian Gulf side) and the east approach zone (Gulf of Oman side) of the Strait of Hormuz.

• Live AIS — Detects when a vessel enters one zone and subsequently appears in the opposite zone within 18 hours. A minimum 6-hour gap between consecutive crossings for the same vessel prevents duplicates.
• GFW historical — Compares each vessel's daily position against a dividing meridian at 56.5°E. If a vessel moves from one side to the other between consecutive days, a crossing is recorded.

Inbound = east → west (entering the Persian Gulf).
Outbound = west → east (leaving toward the Gulf of Oman).

Daily snapshot timing

Each date on the timeline represents a full 24-hour UTC day of vessel detections as aggregated by Global Fishing Watch. There is one record per vessel per day — no duplicates.

Positions are snapped to a spatial grid (not precise GPS coordinates). The location shown is the grid cell the vessel occupied, likely where it spent the most time or was last detected. This means vessels in the same grid cell appear as overlapping markers. The hours field indicates how long a vessel was detected in the area (e.g. 2h = briefly passing through, 20h = anchored or slow transit).

GFW data has a ~5 day lag from the current date. Live AIS positions are real-time but are only merged into dates that already have GFW coverage.

Data sources

Source	Resolution	Coverage
Global Fishing Watch	Daily aggregate	Satellite + terrestrial AIS, SAR
AISStream	Real-time	Terrestrial AIS receivers

Vessels appearing in both sources are deduplicated by MMSI and tagged as "both".

Limitations

• Vessels can disable AIS transponders ("go dark"), especially in conflict zones
• GFW daily positions are aggregated — the exact transit time within a day is unknown
• Small vessels without AIS class A/B transponders are not tracked
• AIS spoofing (false position reports) can occur in this region