Four years ago I wrote about a way to encode the latitude and longitude of any point on the Earth's surface to 10m of accuracy with a 10 character code. Apart from a modification to the way the check digit is calculated, the code remains unchanged.The idea is this: instead of giving people addresses, or coordinates, you can give them something like a post code for any point on the Earth's surface. This can then be entered into a GPS device and decoded. Thus a business can provide its 10:10 code and know that people will be able to find it.I was reminded of this, this weekend when I took the Eurotunnel to France. On their web site they say:Now those latitude and longitude values are very hard to enter, and, although in the UK post codes are pretty accurate, they are not universal (e.g. in France and the US there's no equivalent). In contrast the 10:10 code is global.Here's some JavaScript code that calculates the 10:10 code:The 10:10 code of the Eurotunnel terminal in the UK is: MED 8FV N9K5PS. Many people have pointed out that there are existing systems like this, and existing patents. As far as I am aware, none of them include a check digit. For example, there's the Military Grid Reference System , the Natural Area Code , this Microsoft patent and Geohash . The check digit is critical because it reduces operator error when entering a location on a GPS device.