[ka-Map-users] cache size estimates

Justin George justin.george at gmail.com
Wed May 24 16:17:19 EDT 2006

Since I'm using precache to do all of my generation, I've got an
interesting set of numbers here.

For a shapefile directory size of 2.2GB, the formula to figure out
cache size for a given scale is:

y = 805GB / (3 ^ log2 ( x / 1000)  )

Where y is the final size and x is the scale ratio (1000 for 1000:1)

This doesn't take into account the 'ends' of the scale spectrum:
On the near end, you'll have tiles that are mostly empty and thus
compressed to 113 bytes each (at 200 x 200 tiles)
At the far end, so much will fit into a single tile that it will
overlap enough to decrease the total size.

I'd be interested in hearing your thoughts, it's been a few years
since calculus so I may be a bit rusty at deriving formulas from data.

It's also probably (due to the compression issues above) more like a
logistic curve, but this is good enough to predict my file sizes
between 500,000 and 20,000.

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