What's your position?

September 6, 2006 4:48 AM

Do you know where you are? With Google Maps and Google Earth so commonplace now, GPS everywhere, and with websites such as our own Metafilter making use of latitude and longitude did you ever stop to think about how all this latitude, longitude and height above sea level works? The UK's Ordnance Survey explains it all in A Guide to Coordinate Systems in Great Britain. Discover that different coordinate systems might differ by as much as 200m, and that your house may be moving as much as 1m up and down each day relative to the centre of the Earth, and many other bits of geographical interest.[more inside]
posted by edd (4 comments total)

We've previously heard about the problems of making a 2D map of the Earth, but even working in 3D can leave you scratching your head over simple questions. Depending on how you choose to measure your height on the Earth you may end up deciding that Mount Everest isn't the highest mountain after all.

And difficulties allowing for the curvature of the Earth (a topic all by itself) has resulted in our metre being out by 0.2mm. Cartographers certainly don't have it easy.
posted by edd at 4:48 AM on September 6, 2006

where you at dog?
posted by AaRdVarK at 5:29 AM on September 6, 2006

You can get over a kilometer of shift by using the wrong datum, actually. (Though in this case the greatest shift is between two datums neither of which are intended for use on this continent — if you stick only to British coördinate systems you'll get somewhat better agreement within Britain.)

It always amuses me that computer scientists took the plural (data) and use "piece of data" for the singular, but cartographers took the singular (datum) and formed "datums" from it. It makes sense that it happened that way, but it's still funny.
posted by hattifattener at 9:24 AM on September 6, 2006

:( I'm getting an Adobe error:

Expected a dict object.

Sounds cool, though. I'll check back later.
posted by owhydididoit at 11:32 AM on September 6, 2006