GPS accuracy
GPS accuracy, more precisely GNSS positional accuracy, is how close a recorded coordinate is to the true position on the ground. It depends on the receiver, satellite visibility, canopy, terrain and method, and differs from precision, which is the number of decimals recorded.
Also known as: GNSS accuracy · positional accuracy · horizontal accuracy
Why does it matter?
Plot boundaries are compared against forest maps and neighbouring plots. Positional error can create false overlaps with forest, protected areas or other farmers’ plots, or hide real ones. Accuracy matters most for small plots, where a few metres of error is a large share of the area.
How does it work?
Phones and handheld receivers compute position from global navigation satellite systems (GNSS) such as GPS, Galileo, GLONASS and BeiDou. Accuracy degrades with:
- dense tree canopy, common in cocoa, coffee and agroforestry;
- steep terrain and valleys that block satellites;
- short recording times before a stable fix;
- low-cost receivers and power-saving modes.
Good practice is to store the reported accuracy with each point and use it in quality control. Many programmes combine field walking with digitising on recent high-resolution imagery.
Common pitfalls
- Confusing precision (decimals) with accuracy.
- Jagged, spiky polygons caused by GPS drift, leading to self-intersections.
- Taking a point at the edge of the plot, near the road, rather than inside it.
- No record of which device and method produced the data.
Farmer1st records capture quality and flags implausible geometries for re-mapping through its geo and polygons service.
Frequently asked questions
Does six decimal places mean ten-centimetre accuracy?
No. Six decimals is the precision of the number, about ten centimetres at the equator. A phone under tree canopy may be several metres off, whatever the number of decimals.
How can field teams improve accuracy?
Wait for a stable fix before recording, walk at a steady pace, avoid starting under dense canopy, record the device's reported accuracy with each point, and re-map plots whose polygons look implausible.
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