Slightly offtopic - coordinate conversions

[Chris Jack]

Michael Lush mjlush at ebi.ac.uk wrote:
> On Wed, 13 Jul 2011, Peter Sergeant wrote:
> > I've been playing around with Google Maps recently, and noticed that they've started using hashes of some coordinates:
> >
> > latlng: 52.54296 -0.308166
> > hnear : 0x4877f21032e242f5:0x805cb103d71d5051
> >
> > latlng: 51.411586,-0.300893
> > hnear : 0x47d8a00baf21de75:0x52963a5addd52a99
> >
> > A few attempts at working out how this was done with Perl have failed me - anyone got a better idea?
> 
> Where/why are they doing this?
> 
> I suppose it could be some kind of attempt to obfuscate the numbers in 
> order to prevent 'coordinate harvesting'?

There may be several reasons: and a check sum would certainly help prevent systematic attempts to get 'coordinate harvesting' data (and might suggest an algorithm that was both hard to crack and google might be unwilling to divulge).
 
>From what others have said, it seems to distribute widely and non-linearly - which would be useful for separating data that would otherwise tend to clump around interesting places. So it could also be for efficiency of lookup (the hash is precalculated), you don't get tied in to a set level of coordinate precision, and it maybe even be to help distribute over multiple machines. 
 
Chris