RESEARCH NOTE 01 / ORBITAL TRACKING
What is directly
below the ISS?
The marker on an ISS map is not the station itself. It is the point on Earth that lies directly beneath the station at that moment.
A point projected onto Earth
The International Space Station circles Earth in low Earth orbit, hundreds of kilometres above the surface. Tracking services report its current latitude and longitude as a subsatellite point: the location where a straight line from the station toward Earth’s centre meets the surface.
That is why the map marker can cross a country even though the station is nowhere near the ground. The station is still roughly 400 kilometres above that point, moving at about 27,600 kilometres per hour.
From telemetry to a map
The tracker receives a timestamp, latitude, longitude, altitude, velocity, visibility state, and ground-footprint estimate. Longitude is converted to horizontal position on the map; latitude becomes vertical position. A flat map distorts the globe, so the marker is best read as a useful reference rather than a precise view of the station’s path over curved Earth.
The country label is a separate step. The current coordinates are sent to a reverse-geocoding service, which checks whether that point falls within a country. Over open water, the result is labelled as an ocean and international waters instead.
The ground track is always moving
The ISS completes an orbit in roughly 90 minutes while Earth rotates beneath it. Its path therefore shifts westward from one orbit to the next rather than tracing the same line repeatedly. The station’s orbital inclination also limits the ground track to latitudes between about 51.6 degrees north and south.
The country shown describes the point below the station—not where the station could land, communicate, or be seen from the ground.
Why your view may differ
Telemetry arrives in snapshots. Between updates, the marker is briefly showing the latest known position rather than a continuously measured point. Small timing differences, map projections, network delay, and the rapid orbital speed can make two trackers disagree by several kilometres without either being fundamentally wrong.
To know whether the ISS is visible from your location, a different calculation is needed. A pass predictor combines the station’s orbit with your coordinates, the local horizon, sunlight, and darkness at the observer’s location.