In the United States, three datums are commonly used. NAD 27 CONUS is a 1927-era datum that's most often encountered on old-style maps from the U.S. Geological Survey. Newer USGS maps use NAD 83 ...

For those of us with no real navigation experience, encountering longitude and latitude coordinates is usually the result of some hiccup using Google Maps. 40.722272, -73.994194?

To help locate where a place is in the world, people use imaginary lines called latitude and longitude. Find out more with this year 3/4 BBC Bitesize geography guide.