How Accurate Is Phone GPS for Field Data?

Under open sky, a modern phone usually knows where it is to within 3 to 5 metres. Under forest canopy, near steep slopes or in the first minute after switching on, that grows to 5 to 10 metres or more: enough to find a site or map a plot, not enough to tell apart two young trees planted 3 metres apart.

You can check your own phone, where you work, with our free GPS Accuracy Test. It shows the accuracy in metres as it changes, so you know when it has settled.

What does the accuracy number on my phone mean?

It is a radius. "±4 m" means the phone thinks the true position is probably inside a circle 4 metres around the dot.

"Probably" is doing real work. Android defines the circle so the true position falls inside it about 68% of the time (Android documentation). Roughly one reading in three is farther off than the number says. Browsers, including our test page, report a 95% radius instead, so the same fix shows a larger number there.

The number is also the phone's own estimate. Under trees, or with signals bouncing off a cliff, the phone can be confidently wrong. Treat it as a guide, and check it against something you know on the ground.

How accurate is phone GPS under tree canopy?

Worse than in the open, and it varies more from phone to phone.

• Open sky: GPS-enabled smartphones are typically accurate to within 4.9 metres (GPS.gov).
• Under forest canopy: a 2022 study tested 10 phones at 15 forest sites. Their average errors ranged from 3.7 metres for the best phone to 10.4 metres for the worst. Phones that receive two GPS frequencies averaged 5.6 metres; single-frequency phones 7.1 (Purfürst, Sensors 2022).

That matches what we see with field teams. Phones usually land in the 2 to 5 metre range, and reaching about 1 metre takes an external GNSS receiver that costs $300 to $1,000, plus the work of pairing it with the phone. Some errors are much larger. One team we spoke with found plots mapped in the wrong district, and suspected signal jamming near a border.

Is phone GPS good enough for plots, boundaries and trees?

It depends on the size of what you are locating compared with the error.

Carbon projects raise the bar on boundaries. Verra's ARR methodology, VM0047, treats project area as having no uncertainty, on the condition that boundaries are complete and accurate. There is no allowance for a boundary walked 10 metres off. Many developers draw boundaries on drone or satellite imagery and use phone GPS to check them on the ground.

The last row is the one people learn the hard way. At about 1,100 trees per hectare, trees are 3 metres apart. With a 5 metre error, a point cannot tell you which tree it was. Teams that need to follow individual trees tag them physically, or monitor sample plots instead of single trees.

How do you get a better GPS reading in the field?

• Wait. Give the phone a minute or two with a view of the sky before you record. The first fixes after switching on are the worst.
• Watch the number, not the dot. Record when the accuracy has settled, and record the accuracy with the point, so anyone using it later knows how far to trust it.
• Step into the open when you can: a canopy gap or the edge of a clearing helps. Holding the phone away from your body helps a little too.
• Keep location set to high accuracy in the phone's settings.
• Average when it matters. Several readings taken over a minute or two are steadier than one.
• Use an external receiver when the work needs about a metre or better, such as legal boundaries or tree-level research plots.

How do you test your phone's GPS accuracy?

1. Open the GPS Accuracy Test on your phone, outdoors, and allow location access.
2. Start tracking. The current accuracy shows in metres: green at 5 m or better, yellow up to 20 m, red beyond.
3. Watch the chart for a few minutes, in the open and then under the canopy where you will work. You will see how long it takes to settle and how far it drifts.

You can install the page like an app and use it on site. It runs in your browser and does not send your location anywhere.

How does Restoration Scope handle GPS accuracy?

When a field worker walks a boundary in the Restoration Scope app, the screen shows the current accuracy: green at 10 metres or better, and a "Weak GPS" warning above 25 metres, so they know when the line may wander. The saved shape leaves out fixes that imply an impossible jump. Photos keep the location accuracy their camera recorded, when there is one; what EXIF location data is explains where it comes from.

For choosing an app to collect field data in the first place, see our guide to field-data apps.