2022.08.30 05:43
how many decimal places to write down geographical coordinates
For as long as I can remember, I have had this problem that when I write down geographical coordinates, I don't know how many decimal places to use because I can't recall the (in meters) accuracy for each number of decimal places. Because of this, I tend to write down more decimal places than necessary, just in case. Today, I finally sat down and calculated it. Here are the conclusions:
One degree of latitude difference (i.e., traveling one degree along the meridian) is - regardless of the location on Earth - 111 km. So the first decimal place gives an accuracy of about 10 km (meaning that if I change the digit in the first decimal place by one, the position shifts by 10 km), the second decimal place gives an accuracy of about 1 km, the third decimal place gives an accuracy of about 100 m, the fourth decimal place gives an accuracy of about 10 m, and the fifth decimal place gives an accuracy of about 1 m. So recording latitude with five decimal places means recording with an accuracy of up to a meter.
One degree of longitude difference (i.e., traveling one degree along the meridian) is - for us, in Poland, because elsewhere the navigational deviation will be different - about 67 km. You can even calculate it yourself, as it is 111*cos(53). So the first decimal place gives an accuracy of about 7 km (meaning that if I change the digit in the first decimal place by one, the position shifts by 7 km), the second decimal place gives an accuracy of about 700 m, the third decimal place gives an accuracy of about 70 m, the fourth decimal place gives an accuracy of about 7 m, and the fifth decimal place gives an accuracy of about 70 cm. So recording longitude with five decimal places means recording with an accuracy slightly better than a meter.
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