1. The observation universe
Chokepoint detection draws from the same canonical observation history that supports 7,286 public tanker profiles. Coverage is not uniform: 6,341 vessels currently have a latest observation within one day, while older tracks may contain gaps. Transit counts therefore measure detected crossings in the available observation record, not every physical ship movement worldwide.
This framing matters whenever a headline cites "Hormuz flows". Two sources can disagree by double-digit percentages purely from reception density, observation history depth and deduplication rules - before any methodological difference. Knowing what universe a count comes from is the first step to trusting it.
2. Crossing is different from presence
A vessel near a strait is not automatically a transit. Anchorage clusters outside Fujairah, bunkering stations off Gibraltar, fishing grounds and waiting areas put hundreds of tankers inside broad geographic boxes without any intention of crossing.
A robust detector therefore requires evidence of passage: observations on opposite sides of a defined crossing corridor within a plausible time window, moving in a direction consistent with the corridor's geometry. This prevents anchored ships, coastal traffic and repeated points inside a broad area from being counted as crossings.
The distinction has analytical consequences: presence counts answer "how much activity is near the strait" - useful for congestion and queuing analysis - while transit counts answer "how much trade moved through". Confusing the two produces wildly inflated flow estimates.
3. Direction, event time and AIS gaps
Direction is inferred from the ordered sequence of observations: a vessel seen northbound-entry-side and later northbound-exit-side yields a northbound transit. Each completed crossing receives exactly one timestamp - conventionally the estimated moment inside the corridor - so daily analytics can group, sum and compare days without ambiguity.
Real passages rarely enjoy perfect reception. Narrow straits create shadow zones; dense traffic collides messages; satellites pass intermittently. Gap-aware logic therefore matches entry and exit observations across a bounded window: if a ship disappears entering Hormuz and reappears in the Gulf of Oman within a physically feasible interval, the crossing still counts once. Without that tolerance, every reception dropout would masquerade as a missing transit and undercount flows systematically.
4. How duplicate counts are avoided
Repeated provider messages and dense position tracks can describe the same physical crossing many times. Aggregators stitching feeds from multiple satellites and coast stations routinely double-report identical moments.
TankerMap normalizes observations to canonical vessel identity - keyed on the lifetime-stable IMO number rather than mutable MMSI or name - and stores one transit event per crossing episode. The same vessel may correctly appear again after it leaves, later returns and completes another crossing; it should not appear twice for one episode simply because two providers observed it.
Identity normalization also handles the harder case: vessels that change MMSI or name between the two sides of a passage. Matching on IMO ties the episode together; matching on broadcast strings would count two ships.
5. How to read the charts
Daily values can change when late-arriving positions fill a gap or a replay recomputes the same approved method - a transit detected three days after the fact still belongs to its event date, not its detection date. Compare completed UTC days rather than treating an in-progress day as final, and prefer multi-day trends over single-day headlines.
Segment filters matter too: crude, product and LNG carriers use chokepoints in different proportions, so a mixed count can hide a strong signal in one segment. Open Strait of Hormuz analytics, Suez or the full strait dashboard to inspect current counts by segment and direction.
For the underlying reception concepts - why gaps exist and how identity is maintained - see how AIS tracking works.
6. Frequently asked questions
What counts as a chokepoint transit?
A detected passage: observations of the same vessel on opposite sides of a defined crossing corridor within a physically plausible time window, assigned one direction and one event timestamp. Mere presence near a strait - anchoring, bunkering, waiting - does not count.
Which chokepoints matter most for oil tankers?
The Strait of Hormuz (the largest crude gateway), the Suez Canal and SUMED pipeline route, Malacca for Asia-bound flows, Bab el-Mandeb, Panama and the Turkish Straits. Their relative importance differs by segment: LNG leans heavily on Hormuz and Panama; products distribute through many smaller routes.
Why do different websites show different transit numbers?
Sources differ in reception coverage, observation-history depth, corridor geometry, gap handling and deduplication. A count of detected crossings in one canonical record can legitimately differ from another source's estimate of physical movements - always ask what universe and method produced a number.
Can a transit be missed entirely?
Yes, when reception fails on both sides of a passage or the observation history has holes. Methodologies tune gap windows to balance two errors: missing real crossings versus crediting phantom ones. Published counts describe detected crossings, not certified totals of every ship that passed.