Reading flight tracker maps: symbols, colors and data fields explained

You open the flight tracker app, and over Germany it is teeming with little aircraft symbols. Some are yellow, some orange, some gray, a colorful line trails behind one of them, and the info window shows abbreviations like GS, Baro, Hex or MLAT. If you can read these signs, you get far more out of every map: you can tell whether an aircraft is already on final approach, whether a position is fresh or estimated and whether the aircraft you are waiting for is really the right one. This guide explains symbols, colors and data fields on flight tracker maps step by step – regardless of which service you use.

The short answer

A flight tracker map works with three layers. The symbol roughly reveals the aircraft type and direction of movement. The color means something different depending on the service – on Flightradar24 it is normally uniform, on tar1090-based maps like ADS-B Exchange it stands for flight altitude, on some services for the data source. And the data fields in the info window provide the actual measured values: identifier, altitude, speed, track, squawk and origin of the position.

So the most important rule first: colors are not a worldwide standard. Before you draw conclusions from a color, take a look at the legend or the settings of the respective service. Where the data comes from in the first place is explained in the basics article Flight tracking with ADS-B for spotters, and which services exist is covered in the flight tracker apps comparison.

The symbols: silhouette and direction

Most big services do not simply draw dots but silhouettes. Based on the ICAO type code stored in the database for each aircraft, the map picks a matching symbol: a four-engine widebody jet for the Airbus A380, a slim twinjet for the Airbus A320neo, plus separate shapes for turboprops, business jets, helicopters or gliders. If the type is unknown, a generic symbol appears. How to find rescue and police helicopters specifically is shown in the guide Tracking helicopters on the flight tracker.

A limitation follows from this: the icon is only as good as the database behind it. If an aircraft is entered incorrectly or not at all, you see a mismatched symbol. You therefore read the reliable type from the type code in the info window, such as A20N, B38M or B77W. What lies behind these abbreviations is explained in the article ICAO type codes explained.

The orientation of the symbol usually follows the track, meaning the ground track. That is the direction the aircraft is actually moving over the earth. The heading – the direction the nose points – differs from it in a crosswind. If you see a jet on approach with a clear crab angle, you do not necessarily notice that on the map, but you do in the info window of some services, if both values are shown separately.

Special cases on the ground

At the airport, symbols sometimes appear that are not aircraft at all. Some airports equip vehicles such as tugs or apron vehicles with their own transmitters, which can appear on tar1090-based maps as a ground vehicle category. Aircraft that are parked or taxiing are shown gray, smaller or not at all depending on the service – many services hide parked aircraft after a while without movement.

Colors: three different systems

The most confusing thing about flight tracker maps is the colors, because each service uses its own system. At its core there are three approaches.

Color system	Typical example	What the color says	What to watch out for
Uniform color	Flightradar24	Nothing about altitude or type – only “being tracked” or “selected”	Altitude is in the colored trail and the info window
Color by altitude	tar1090, ADS-B Exchange	Flight altitude from low (warm) to high (cold/violet)	Gray stands for ground or unknown altitude
Color by source	Setting on some services, table colors in tar1090	whether ADS-B, MLAT, satellite or another source	The source says something about accuracy and currency
Highlighting	almost all services	Selection, filter hit or emergency squawk	Highlighting is no proof of a real emergency

Flightradar24: yellow simply means “live”

On Flightradar24 the symbols are yellow by default, regardless of altitude or airline. The color only means that the aircraft is being picked up through the receiver network. If you click an aircraft, it is highlighted, and the flight trail appears behind it. This trail is colored by altitude: from the color gradient you see at a glance where the aircraft climbed or descended. How to use the interface in detail is shown in the Flightradar24 guide.

tar1090 and ADS-B Exchange: color is altitude

The open-source interface tar1090, on which the map of ADS-B Exchange is also built, colors aircraft by altitude by default. According to the project’s example configuration, the hue at 2,000 feet is orange, at 10,000 feet light green and from 40,000 feet violet/magenta; in between it is interpolated continuously. Aircraft on the ground are dark gray, aircraft without altitude data light gray.

In addition, tar1090 slightly changes the base color: positions from MLAT are shown somewhat darker and paler, outdated positions considerably lighter. That is subtle but useful – a conspicuously pale symbol often has not delivered a fresh position for a while. If you use tar1090 with your own receiver, you will find more in the guide Flight tracking on the desktop with tar1090.

Color by data source

Some services let you color the symbols by source, and tar1090 colors the table rows in the list view by data origin: ADS-B, MLAT, TIS-B or other get different pastel shades, and UAT and satellite share one hue in the default configuration. On Flightradar24, aircraft whose position comes from satellite data appear blue instead of yellow. Which source lies behind which color is again revealed only by the service’s legend.

The identifiers: four names for one aircraft

The header of the info window usually shows several designations. Mixing them up is the most common beginner mistake.

• Callsign: the identifier under which the flight runs on the radio and in the transponder, for example an ICAO airline code plus a number. It belongs to the flight, not the aircraft. Why it often looks different from the number on your ticket is explained in Callsign and flight number: the difference.
• Flight number: the commercial number with the airline’s IATA code, as it appears on departure boards. Background on the two code systems is provided by the article IATA and ICAO codes explained.
• Registration: the official registration on the outside of the fuselage, for example with D- for Germany. For spotters the most important detail, because it designates the individual aircraft unambiguously. More in Understanding aircraft registrations.
• Hex code (ICAO 24-bit address): the six-digit hexadecimal address of the transponder. It is permanently assigned to the aircraft and is the key services use to look up registration and type in their database. What lies behind the six characters is covered in the article ICAO hex code explained.

An aircraft often flies several flights a day with changing callsigns but keeps its registration and hex code. If you are waiting for a specific aircraft, you therefore always search by registration or hex code – never by flight number. How that works in practice is explained in Tracking an aircraft by registration.

The measured values: altitude, speed, track

Altitude: barometric or geometric

The standard altitude figure is almost always the barometric altitude. The transponder reports what the altimeter would show with the standard pressure of 1013.25 hPa set – in cruise this corresponds to the flight level: 35,000 feet is FL350. If the actual air pressure differs from the standard, the true height above sea level is above or below it. Near the ground, in a high- or low-pressure system, that quickly adds up to a few hundred feet.

Some services additionally show a geometric altitude (GPS or WGS84 altitude), which comes from satellite navigation. It is normal for the two values to differ. What matters for you at the spot: neither figure is the height above ground. At an airport at 1,500 feet elevation, a landing aircraft just before touchdown does not read zero.

Speed: over the ground or through the air

Field	Abbreviation	Meaning	Use for spotters
Ground speed	GS	Speed relative to the earth, in knots	Estimating the arrival time at the spot
True airspeed	TAS	Speed relative to the surrounding air	The difference from GS shows tailwind or headwind
Indicated airspeed	IAS	Value shown by the airspeed indicator in the cockpit	Relatively constant on final approach, depends on type
Mach number	Mach	Fraction of the speed of sound	Interesting in cruise, hardly relevant at the spot

One knot equals 1.852 km/h. For the spot, ground speed counts most: in a strong headwind an approach takes noticeably longer to reach the runway than in calm air. How reliable the arrival times calculated from it are is examined in the article How accurate are ETA predictions?.

Vertical rate, track and squawk

The vertical rate in feet per minute reveals whether an aircraft is climbing or descending. A steady descent along the runway axis is a clear sign of the final approach, as described in the article ILS approach explained. If the rate jumps to positive just before the runway, that is a typical sign of a go-around.

The squawk is the four-digit transponder code assigned by air traffic control. Each digit can only take the numbers 0 to 7, which gives 4096 combinations. Three of them are reserved for emergencies: 7500, 7600 and 7700. Many services highlight such codes in color; in the tar1090 configuration, for example, red (7500), cyan (7600) and yellow (7700) are provided. What the codes mean exactly and why you should not read too much into them is covered in the guide Squawk codes 7500, 7600 and 7700.

The data source: the underrated field

Almost every service reveals somewhere where a position comes from. For your assessment this is the most important field of all.

Besides the source, technical interfaces like tar1090 also show when the last position was received. A value of a few seconds is fresh; a value of a minute or more means: careful, the aircraft may long since be somewhere else. Further fields like signal strength (RSSI), message rate or accuracy values (NACp, NIC, SIL) you need mainly if you run your own receiver. If an aircraft does not show up at all, it is often due to the source or filters – the most common reasons are collected in the article Why an aircraft does not appear on the flight tracker. Which kinds of transponders exist at all is explained in Mode S transponders explained.

Reading the flight trail correctly

The line behind a selected aircraft is more than decoration. It shows the path of the last minutes or of the whole flight and is colored by altitude on the big services. A few patterns repeat constantly:

• Straight line onto the runway axis, even color gradient: stable final approach. In Frankfurt or Munich you often see several aircraft in a row on parallel axes this way – for example from the Munich Airport visitors’ hill.
• Oval or racetrack shapes: a holding pattern. What lies behind it is explained in the article Holding explained, and how to recognize it on the map is shown in Recognizing holding patterns on the flight tracker.
• Loop just before the runway with renewed climb: go-around, details under Go-arounds explained.
• Patchy or jumpy trail: changing data sources or reception gaps, often at low altitude far from receivers.

Incidentally, you read which runway is currently in use faster from the trails than from any table. How the runway direction in use follows the wind is described in the guide Understanding runway direction in use at airports – at airports like Frankfurt Airport or Munich Airport it decides which spot is worthwhile.

Common misreadings

• “Gray means out of service.” Depending on the service, gray means on the ground, altitude unknown or outdated – not broken or decommissioned.
• “The icon shows exactly where the nose points.” It mostly shows the ground track. In a crosswind this does not match the longitudinal axis.
• “Altitude 2,000 ft means 600 meters above me.” The figure refers to sea level or standard pressure, not to the terrain at your spot.
• “An emergency squawk means danger.” Codes are also set by mistake, and many emergencies are medical. The map does not replace official information.
• “The map is live.” Depending on the service, source and region, there are delays from seconds to minutes. Some data is deliberately delayed or filtered.

How to read an aircraft in ten seconds

With a little practice, reading becomes routine. At the fence a fixed order is enough:

1. Check registration and type code – is it really the aircraft you are waiting for?
2. Look at altitude and vertical rate – if it descends steadily, it is on approach.
3. Estimate ground speed and distance – how many minutes are left?
4. Check data source and age of the position – is the information fresh and accurate?
5. Look at the trail – does the direction match the runway you are standing at?

Conclusion

Flight tracker maps are no riddle if you separate the three layers: the symbol shows type and direction of movement, the color follows the system of the respective service, and the actual facts are in the info window. For spotters, what counts there is mainly registration, type code, altitude, ground speed and the data source. If you get into the habit of looking at the legend first on every map and briefly at the source for every aircraft, you will rarely be surprised by a wrong symbol or an outdated position.