When a plane disappears from the map, it hasn't necessarily disappeared from the sky

AI illustration: a tabby cat watching planes at sunset
Illustration: AI

ADS-B Exchange vs adsb.lol

Aircraft maps are a wonderfully efficient way to lose twenty minutes. You open one to identify a plane overhead and end up following another plane you have absolutely no reason to care about. Meanwhile, the laundry waits. At least it stays within reception range.

I picked ADS-B Exchange and adsb.lol because both let us explore aircraft movements. The interesting comparison, though, starts with what they don't show. A screen full of aircraft icons looks convincing. It still isn't a complete inventory of the sky.

What are we actually seeing?

ADS-B broadcasts let suitably equipped aircraft report information such as position, altitude and speed. Receivers pick up those broadcasts, and a network displays the data it receives. Some positions are calculated using MLAT: several receivers compare signal arrival times to work out where the aircraft is.

This isn't an air traffic control display. Nor is it an attendance sheet for every aircraft in the world. Suitable transmissions, reception and usable data all matter.

ADS-B Exchange: start exploring

The map at globe.adsbexchange.com opens without an account. Zoom into an area, select an aircraft, examine its details or try the search and filters. There's plenty to investigate and plenty of buttons. If a click makes the aircraft vanish, check your filters before announcing a worldwide pilots' holiday.

Ordinary map viewing is free, with ads. An individual ad-free subscription starts at $2.99 a month. That pays for the map experience, not unrestricted access to data for your own application.

The separate Community API costs $10 a month for 10,000 requests and is for non-commercial use. An API lets one program request data from another. Commercial use needs a different licence, and seeing information on the map doesn't automatically give you permission to redistribute it.

adsb.lol: an appealing starting point for builders

adsb.lol also has a free map you can open without an account. My particular interest is its public API: you can request aircraft data for free, currently without an API key.

Its public data is offered under ODbL, an open database licence that allows commercial use subject to conditions. These include attribution and, where applicable, sharing an adapted database under the same licence. That does not automatically mean every application must be open source. It also does not mean "anything goes".

Free isn't the same as unlimited. Request limits change with load. The documentation says a future key may require contributing receiver data, and asks developers to get in touch before using the API in production. It's an attractive place to experiment. A service that must stay available needs more homework than checking the price.

AI illustration: a cat pointing at a search radius on a map
Illustration: AI

The trap: a valid answer can still be a partial picture

There are three separate limits worth keeping apart:

  • Reception coverage. The networks do not necessarily hear the same aircraft. Receiver locations, aircraft altitude and reception conditions affect what reaches them. Zooming in cannot invent a receiver where reception is missing.
  • The question you asked. A query around a point returns aircraft within the requested area that the network knows about. adsb.lol documents its area query up to a radius of 250 nautical miles. That's not a request for the entire sky, even if the response arrives without an error.
  • What the display shows. ADS-B Exchange's help says its aircraft list is limited to about 100 entries. It separately documents a 100-aircraft display cap on mobile. A wide view can leave things out even when the system has the data. Zoom in, and don't treat the sidebar as a census.

A short result list therefore doesn't prove that few aircraft are flying. A missing aircraft doesn't prove deliberate blocking, either. It may be outside your query, outside reception coverage, missing a usable position or absent from the current display.

Let's try it

Open both maps, zoom into the same area and check for filters that narrow the results. Select an aircraft and compare its details and the age of its update where shown. Don't declare a worldwide coverage winner from one count: place, time and settings matter.

For API experiments, also check the query's centre, radius, filters and data timestamps. An empty successful response isn't a server error; a server error isn't evidence of an empty sky. And an old position doesn't become current just because its icon looks enthusiastic.

Noa's verdict

For a curious browse, I'd start with ADS-B Exchange and keep adsb.lol open as a second view. For experimenting with aircraft data in a small project, adsb.lol is my first choice thanks to its free API and open data licence, provided you accept the terms and service limits.

A warm recommendation for both. A very cold recommendation for "I can't see it, therefore it isn't there". These are windows onto the sky, not the sky itself. Neither should replace navigation tools or authoritative safety information.

Try them: https://globe.adsbexchange.com/ | https://adsb.lol/

For builders: https://api.adsb.lol/docs

A small glossary before take-off

  • ADS-B: broadcasts from suitably equipped aircraft carrying information such as position, altitude and speed. Ground receivers must pick them up for them to appear in the network's data.
  • MLAT: calculating a position by comparing when the same signal reaches several receivers. Useful when the signal doesn't directly include a position.
  • API: a way for one program to request data from another, without someone copying it off the map.
  • Query: a request for data matching particular conditions. For example, "Which aircraft does this network know about near this point?" The answer is limited by what you asked and what the network knows.
  • Radius: the distance from the centre point to the edge of the search circle. Check both the number and the distance unit.
  • Coverage: the places and conditions in which the network can receive data. A coverage gap isn't evidence of an empty sky.
  • Filters: settings that narrow the display, such as altitude or aircraft type. A filter can hide an aircraft from view even when it exists in the data.
  • Timestamp: a record of when the data was updated. An old position tells you where the aircraft was, not necessarily where it is now.
  • ODbL: an open database licence used for adsb.lol's public data. It allows use subject to conditions, including attribution and sharing an adapted database where the share-alike requirement applies. "Open" doesn't mean "no conditions".

Humour note: the laundry and pilots' holiday jokes are jokes. Unfortunately, the coverage and query limits aren't.

In Hebrew: כשהמטוס נעלם מהמפה, הוא לא בהכרח נעלם מהשמיים

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