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As part of checking some prereqs for an idea (IOS app with MBtiles on local storage enabeling offline maps) I'd like to know if it's useful to gzip MBtiles when transporting them to an IOS device.

In other words, is there a useful reduction in size when gzipping MBtiles? (or is the MBtile-format, already packed in some way, thus limiting the use of gzip or other packers). If so, how much size reduction can I expect? (percentage ballpark)

Thanks, Geert-Jan

NOTE: crosspost from SO (as it's within both domains) http://stackoverflow.com/questions/13864691/what-size-reduction-can-i-expect-on-average-when-gzipping-mbtiles

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If it's exported from TileMill, it'll be small - less than 15% on average, since you're dealing with PNG compression (internally similar to gzip) as well as a duplicate tile dictionary.

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Thanks for responding here Tom. Question was meant generally, but I'm particularly thinking of the default Mapbox streets layer. So I guess I'm talking to the right person ;). Just realized (duh) that I could just inspect my client request/responses to get some real feel of sizes. 25KB/tile for levels 13-16 and 15-20KB/tile for level 17 seems to be average. And being served as png indeed no use for gzip. Checking now if (guessing yes) untoggling buildings makes a big impact on size. Thanks. –  Geert-Jan Dec 13 '12 at 17:44
    
yup.. disabling buildings -> ~6KB/tile on level 17. great –  Geert-Jan Dec 13 '12 at 17:51
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