Map tile format r&d, based on resolutions

image format test results

JPEG / No Imagery / Fresh Cache

250000 - 196.5k
150000 - 212.8k
100000 - 1.2m
80000 - 1.2m
50000 - 1m
35000 - 831.1k
32000 - 735.1k
25000 - 772.8k
10000 - 399.9k
5000 - 221.3k
2500 - 108.5k
700 - 81.2k
350-25 - 81.2k

PNG / No Imagery / Fresh Cache - believe this is similar to png24

250000 - 140.1k
150000 -140.2k
100000 - 1.2m
80000 - 1.1m
50000 - 919.5k
35000 - 775.6k
32000 - 647.3k
25000 - 498.8k
10000 - 252.9k
5000 - 146.2k
2500 - 56.1k
700 - 40.3k
350-25 - 40.3k
!beats jpeg at every level

PNG8 / No Imagery / Fresh Cache

250000 - 57.5k
100000 - 356.6k
700-25 - 13.6k
!beats jpeg and png at every level at a significant level

PNG32 / No Imagery / Fresh Cache

250000 - 143.5k
100000 - 1.2m
700-25 - 41.7k

GIF / No Imagery / Fresh Cache

250000 - 63.3k
100000 - 391.4k
700-25 - 12.4k <- little better than png8 at this level

BMP / No Imagery / Fresh Cache

250000 - 12.4m
100000 - 12.4m
700-25 - 12.4m
!always 12.4m regardless of color information

TIFF / No Imagery / Fresh Cache

Not viewable in browser

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JPEG / Imagery / Fresh Cache

35000 - 1.4m (when imagery first turns on)
32000 - 1.3m
25000 - 1.3m
10000 - 982.9k
5000 - 722k
2500 - 409.9k
700 - 212.1k
350 - 176.5k
175 - 136.1k
75 - 108.4k
50 - 99.7k
25 - 92.5k

PNG / Imagery / Fresh Cache

35000 - 6m
32000 - 6.1m
25000 - 5.8m
10000 - 5.3m
5000 - 4.4m
2500 - 2.6m
700 - 333.7k
350 - 143.4k <- png starts beating jpeg
175 - 80.2k
75 - 54.3k
50 - 49.3k
25 - 44.9k

PNG8 / Imagery / Fresh Cache

35000 - 1.8m <- jpeg still wins
32000 - 1.8m
25000 - 1.8m
10000 - 1.7m
5000 - 1.6m
2500 - 1.3m
700 - 899.8k <- png is better than png8 here
350 - 624k
175 - 384.1k
75 - 36.1k <- png8 starts beating png again
50 - 29.9k
25 - 25.4k

PNG32 / No Imagery / Fresh Cache

35000 - 6m
32000 - 6m
25000 - 5.8m
10000 - 5.3m
5000 - 4.4m
2500 - 2.6m
700 - 333.2k
350 - 142.9k
175 - 79.8k
75 - 54k
50 - 44.2k
25 - 44.4k
!almost the same results as png

GIF / Imagery / Fresh Cache

35000 - 2.2m <- png8 better, jpeg still best
700 - 815.8k
25 - 73k
!png8 whips on all accounts

BMP / Imagery / Fresh Cache

250000 - 12.4m
100000 - 12.4m
700-25 - 12.4m
!well at least bmp is consistent

TIFF / Imagery / Fresh Cache

Not viewable in browser

ol enhancements

having as few layers a possible, ideally one wms layer
setting buffer: 0, to not request additional images outside the viewport
making the layer hidden until needed (so not requesting images on accident that are nothing)
multiple wms servers, three seems to be a good number
using wms/tilecache sharing the same wms layer (since both won't be on at the same time)
png8 image format is a clear winner for vector layers (no imagery), although some pigmentation changes noticed
jpeg seeems to be most ideal for imagery

in general, the more different colors on the map styles, the more time to download