GPS coordinates digit precision

Since Earth equatorial circumference is around 40000 km and longitude spans 360 degrees, it follows that near the equator 1 degrees is equivalent to about 110 km.

Thus:

0 digit precision: ±110 km

1 digit precision: ±11 km

2 digit precision: ±1.1 km

3 digit precision: ±110 m

4 digit precision: ±11 m

5 digit precision: ±1.1 m

6 digit precision: ±11 cm

7 digit precision: ±1.1 cm

However, the closer you move to the Poles, the smaller the lenghts of the parallels becomes.

For example near Rome, which has a latitude of 42 degrees 1 degree is equivalent to cos(90-42)*110= 74 km.

Thus:

0 digit precision: ±74 km

1 digit precision: ±7.4 km

2 digit precision: ±0.74 km

3 digit precision: ±74 m

4 digit precision: ±7.4 m

5 digit precision: ±0.74 m

6 digit precision: ±7.4 cm

7 digit precision: ±0.74 cm