Accuracy depends on the device, measurement method and conditions. A precise-looking number does not mean the boundary is equally precise.
Map, phone GPS and RTK
- Map points depend on image alignment, age and how clearly you can identify the boundary. Zooming in does not correct a shifted image.
- Phone GPS generally has meter-level uncertainty, which can worsen near trees and buildings. See GPS.gov’s accuracy explanation.
- RTK can provide centimeter-level positioning with a suitable receiver, current corrections and a stable fixed solution. Receiver setup, sky view and the reference frame matter. Point accuracy is not a guarantee of the same area accuracy. See RTK requirements.
What the ± estimate means
For GPS measurements with usable accuracy data, the app estimates uncertainty from the reported point accuracy and the geometry. The GPS quality summary shows the accepted and ignored points, plus average and worst reported accuracy.
This is a rough estimate, not a measured error against a surveyed reference or a guaranteed confidence interval. Small or narrow plots are more sensitive to boundary errors. Moving GPS points on the map also changes the basis of the result.
Improve the recording
Use a clear sky view and pause at corners. Choose Strict, Balanced or Relaxed in GPS quality settings; the app shows the thresholds. A more relaxed setting accepts weaker fixes; it does not improve them. See GPS measuring.
Compare on a known plot
- Use an independently measured reference boundary. Record how the reference was obtained.
- Record the phone or receiver model, date, sky conditions, method and RTK fix status if applicable.
- Repeat the same boundary at least three times. Save each result and its quality summary.
- Compare area with the reference: absolute difference ÷ reference area × 100%. Keep all results, including poor ones.
Repeatability alone does not prove accuracy: a shifted boundary can repeat consistently. The examples and screenshots on this website use sample data and are not outdoor accuracy tests.
Use the result appropriately
Use the app for planning and estimates. It does not establish legal property boundaries or replace a licensed surveyor.