The Earth's circumference (at the equator) is 40,075.02 km. That means that one degree of longitude is 111.3195 km. Geographers typically represent longitudes and latitudes to four decimal places, so the smallest discernible measurement is 0.0001 degrees, or about 11 metres. And that's at the equator. Away from the equator the measurements get finer. So four decimal places is a pretty good level of detail.