Measuring 39S with Google Maps

Google Maps is accurate for measuring distances. If it wasn’t, we would know since billions of trips rely on its accuracy for driving directions.

To measure the entire circumference of a line of latitude you can measure a section of the line of longitude and multiply by the appropriate factor to get the entire circumference.

Below we see that from -39, -73.3163 to -39, -62.312346 is 950.32km according to Google Maps.

This is a difference of 11.003954° longitude. This is 3.05665% of the circumference of the line of latitude.

To get the entire length of the line of longitude:

360° / circumference = 11.003954° / 950.32km

( 360° * 950.32 ) / 11.003954° = c

c = 31,101.38 km

The circumference of the equator is 60 Nautical miles * 360 = 21,600 Nautical miles = 40,003.2 km

The circumference of 39°S Latitude is less than the equator. This is mandatory on a globe.