GPS Accuracy vs Precision: What Is the Difference?

Accuracy describes how close a measured location is to the true location. Precision describes how consistent repeated measurements are with each other, or how many digits a value is written with. A location can be precise without being accurate, and it can be written with many digits without being either.

The dartboard picture

Imagine throwing darts at a target.

• Accurate and precise: all darts land tightly clustered in the bullseye.
• Precise but not accurate: all darts land close together, but away from the bullseye.
• Accurate but not precise: darts are scattered widely but average out around the centre.
• Neither: darts are scattered and off-centre.

For GPS, the bullseye is your real position, and each reading is a dart.

Accuracy in practice

Phone and consumer receivers typically report an accuracy figure along with the position. This is an estimate of how far the real position may be from the reported point, often drawn as a circle around the blue dot on a map. In open sky, many phones are within a few metres. Near tall buildings, under dense tree cover or indoors, the circle can grow to tens of metres or more. The causes are covered in why phone GPS is inaccurate.

Precision in two senses

The word precision shows up in two ways:

1. Repeatability: if you stand still and record several readings, how tightly do they group? Small scatter means high precision, though a constant bias can still shift the whole group.
2. Numeric precision: how many decimals a coordinate is written with. This is about format, not truth. A value with nine decimals suggests sub-millimetre detail even if the device could only be trusted within metres. The decimal places guide explains the distances involved.

Why it matters for addresses and delivery

When someone shares coordinates, ask what they came from. A pin dropped on a map after zooming in carefully can be more reliable than a phone reading taken indoors, even if both have the same number of decimals. For tasks such as locating a doorway, a deliberately chosen map point is often the better source.

Using this idea with grid codes

A grid code gives a fixed resolution: all points within the same cell share one code. UPCS cells are 3 m by 3 m. The code always resolves back to that exact square, so for the best result zoom in and pick the real entrance. Read why a 3 metre grid cell is practical for the reasoning behind that size.