Wednesday, August 18, 2021

What Two Numbers

Yesterday Mapbox announced that they were integrating the controversial global addressing system What3Words with their Mapbox Dash navigation system.This immediately led to a lot of people on Twitter to question why Mapbox don't just use the latitude and longitude geographic coordinate system. You know the coordinate system which Mapbox uses in its own mapping APIs. 

The latitude and longitude system has the benefit of using two numbers instead of three words. It also has the advantage of being able to provide geographic accuracy to the molecular level - as explained in this xkcd strip. It is also completely free to use and universally accepted and understood.

Yesterday, completely incidentally, Vladimir Agafonkin released an Observable notebook which visualizes the accuracy of the latitude and longitude geographic coordinate system when using increasing numbers of decimal places. His Latitude and Longitude Precision visualization overlays a red square on top of a map to show the area of the world that a latitude and longitude number points to.

Using two numbers to 4 decimal places you get an address with roughly the same accuracy as what3words. However if you add more numbers to your latitude and longitude address you can get even greater accuracy. Use two numbers to 6 decimal places and you can point to any location on Earth that is about ten centimeters square in size. What's more if you cut and paste a latitude and longitude into the search box of any interactive map it will instantly show you the location with that latitude and longitude address.

1 comment:

Anonymous said...

Two problems: people don't know what precision is required (if the device shows ten significant figures they must be important!). Second HMS confusion.

About ten years ago I called in a 911 call in the nearby woods and my GPS was set to decimal. The dispatcher insisted that what I was telling them was not possible. Had to be HMS. I tried to tell them that a helicopter pilot would understand decimal degrees. (I wasn't sure of that but 10 years ago, standing in the hot sun with an injured friend, I didn't want to try to convert.

w3w seems unlikely to succeed in many places. Particularly since different word are used in different languages. Which language is used in an officially multi-lingual country like Switzerland? Etc.