Yes, I have and it worked great! You have to enable the labs feature called "Pre-Cache Map Area" and it's a bit annoying that it will only let you grab a few (10) chunks at a time, but I used it last month while traveling 100 miles from "civilization" and it worked great.
TileMill doesn't seem particularly well suited for that either. I did a rough calculation and it looks like getting a usable map of Washington D.C. would run several hundred gigabytes. I'm wondering if the only way to do something like this realistically on a mobile device is to move the rendering to the client.
The first is 17MB, the second is 57MB. One could probably get to sidewalk-level without cracking 1GB here. Where did hundreds of gigabytes come from?
That said - we'd like to start doing rendering on-client, and it would be great - the question is how to slice and dice data so that the data itself isn't gigantic and rendering it isn't slow.
I probably made a mistake when estimating this. I exported 21 tiles to MBTiles at 429KB, and extrapolated based on the 5.7 billion tiles it would take to do D.C. at 13-16.
I'm still waiting for a larger job to complete, so I don't have a sense of the file size there.
Edit: Got it. The default export is the entire world. Whoops.
Though perhaps not optimized for an urban solution like DC, we have done work around tile de-duping and tile data compression to combat things like this.
