[Talk-GB] invisible

Henry Gomersall heng at cantab.net
Thu Jan 20 13:56:23 GMT 2011

On Tue, 2011-01-18 at 21:37 +0000, Graham Jones wrote:
> The map tiles for the canal map I just generated take up 2.4GB (down
> to zoom level 14). I just extracted the canal data from the database
> (lines, points and polygons) and as a simple text file it was less
> than 57MB.   Gzip compression took it down to just over 17 MB. ie a
> factor of over 100 when compressed. 
> This is not really a fair comparison though because most of my 2.4GB
> is taken up by blank tiles (tiles with no canal features in) - these
> are each 116 bytes.   I am sure I could do something clever with
> having one image and lots of symbolic links which could reduce this
> significantly - better than say a factor of 10, but I don't know if I
> would get to 100.   But that said, the difference was not as big as I
> expected it to be - good challenge! 

That all sounds interesting. What format are the tiles in?

I will put my hand to helping when I have a little amount free.

Good work!



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