GPS Accuracy While Spotting: Why Your Pin Is in the Wrong Place

Updated: August 2026 – You save a spot at the end of the platform, and the map drops the point right on the neighbouring track or in front of the station entirely. This guide explains why your phone’s GPS accuracy collapses at exactly the most interesting locations – and which simple tricks make your position data usable again.

How accurate is GPS on a phone, really?

Under a clear sky, a current smartphone’s positioning is typically accurate to within a few metres. As soon as the view of the sky is restricted – under a platform roof, between tall buildings, in an underpass – the error can grow to several dozen metres. Accuracy isn’t a property of your device, it’s a property of your location.

That explains the common observation that the same phone works to within a metre out in the countryside and is completely off in the main station. Anyone logging sightings and spots should plan for this fluctuation rather than fight it. How strongly this affects the display on maps is easy to see in the features of the Trainspotter Map, where sightings and locations come together.

The four causes of incorrect positions

A GPS receiver measures nothing but travel times. It calculates how long the signals from several satellites took to reach it, and derives its location from that. Anything that distorts these travel times or blocks satellites shifts the result.

Multipath effects: the main suspect on the platform

If a signal doesn’t arrive directly, but after reflecting off a station roof, a glass façade or the side of a vehicle, it has taken longer to arrive. The receiver interprets the longer travel time as a greater distance. The result isn’t random noise, but a systematic offset in a particular direction – which is why the pin often lands reproducibly on the same wrong track.

Shadowing: too few visible satellites

For a three-dimensional position, the receiver needs at least four satellites. Under a platform roof or in a narrow street it may see only a few more than that – and they all sit within a narrow strip of sky. This unfavourable geometry worsens accuracy even when enough signals are getting through.

Cold start: the first few seconds lie

Without current orbital data, the device first has to receive it. Until then it delivers either no position at all, or a roughly estimated one, often derived from mobile cells and Wi-Fi networks. It’s exactly during this phase that many people save their spot – and wonder later why it’s wrong.

Compass and sensors: direction, not location

The heading your app shows doesn’t come from the satellites, but from the magnetic sensor. Overhead line masts, railings, vehicles and even magnetic clasps on a camera bag or phone case throw it off. Anyone documenting light direction, as recommended by the railway photography guide with tips and locations, should calibrate the compass beforehand.

Symptoms and remedies at a glance

Symptom	Likely cause	Immediate fix
Pin lands on the neighbouring track	Multipath effect under the station roof	Move the pin manually, cross-check against your photo’s viewpoint
Position jumps around while walking	Changing shadowing between buildings	Stand still, wait 30 seconds, then save
Location stays rough for minutes	Cold start with no current satellite data	Open the maps app, find open sky, wait
Direction arrow spins wildly	Disturbed magnetic sensor	Calibrate the compass, keep away from metal
Altitude is obviously wrong	Geometrically weak altitude fix	Ignore the altitude or read it off the map
Position is completely wrong on a train	Vehicle roof shields the signal, movement hinders the fix	Hold the phone by a window, check the position after getting off

Checklist: how to get the best possible fix

Correcting the pin manually: the most reliable method

Every trick for improving the signal shares the same limit: none of them can change the physics of the surroundings. The only method that always works is correcting it by hand.

Anyone who records their spots in a structured way already does this step automatically. What a complete entry looks like is covered in the guide to creating your own photo-spot map.

When accuracy matters – and when it doesn’t

Not every use case needs the same precision. This breakdown saves you frustration.

Anyone collecting lots of observations quickly notices: for analysis, consistency matters above all. How a usable picture emerges from many individual reports is shown in the overview of live sightings in real time – and how location data behaves on local public transport is explained in the guide to real-time bus tracking.

Android and iOS: where the differences really lie

The question “which system locates better” is misleading. What matters isn’t the operating system, but the combination of the receiver chip, the antenna’s position within the casing, and which additional sources the device is allowed to draw on.

Three things make the practical difference:

• Dual-frequency reception. Newer mid-range and high-end devices receive two frequency bands at once. That specifically defuses multipath effects, because reflected signals behave differently in each band and can be calculated out. On a platform between a station roof and a noise barrier, this is the single most noticeable factor.
• Network-assisted positioning. Both systems draw on Wi-Fi networks and mobile cells for support. That speeds up the first fix considerably, but in densely built-up areas it can also introduce an offset if a network’s stored position is out of date. Anyone recording a spot permanently should therefore never set the point right after switching the phone on.
• Power-saving modes. As soon as the screen is off or battery-saver mode kicks in, both systems throttle how often they update location. That doesn’t matter for a one-off location report, but it does for a continuous recording.

One more point often gets overlooked: the accuracy figure shown in the app is itself an estimate. It describes a radius within which the true position is highly likely to lie — not the actual error. A reading of “±8 m” doesn’t mean you’re eight metres off, but that the device estimates its own uncertainty at that level. With strong reflections, the real error can be much larger while the displayed figure still looks good. So when in doubt, rely on a visual comparison with the map rather than on the number.

What to watch out for

• Don’t trust the first reading. The position right after opening an app is often estimated from network data rather than satellite-based.
• Read the accuracy indicator if there is one. Many apps show a radius. If it’s larger than the distance to the neighbouring track, the automatic position is worthless.
• Avoid metal when calibrating. Right next to an overhead line mast or a steel railing, the compass will never calibrate cleanly.
• Check battery-saver mode. Aggressive power-saving options throttle location services in the background and noticeably slow down every fix.
• Add the position afterwards if needed. If things were hectic on site, correct the entry the same day – after a week you won’t remember exactly where you stood.
• Use consistent reference points. Anyone who always places spots at the platform end, or always at the access gate, gets comparable data. How helpful that is at large stations is shown in the overview of the best stations for trainspotting.

Conclusion

GPS accuracy while spotting isn’t a device problem, it’s a location problem. Station roofs, urban canyons and underpasses produce systematic errors that you can neither click away nor buy your way out of. What helps is a routine: find open sky, wait, check the pin and drag it to the right spot by hand if in doubt. Anyone just starting out will find the right basics in the tips for new trainspotters, and anyone wanting to bring locations and sightings together neatly will find the framework in the Trainspotter Map.