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Disclaimer: I don't know anything about maps, please excuse me.

In our mobile app, we use Cloudmade as our map tiles provider. For certain places, we download multiple tiles for each zoom level (level 13 through 19) to be used offline.

The thing is that sometimes you need to download tiles for thousands of places at once, making it a very lengthy download.

We are trying to optimize this process and there are a few things that I've come up with, which I don't know if they even make sense:

  1. Cloudmade serves the tiles as png files. We could try to cache those tiles in our server, and reduce their size.
  2. Skip some zoom levels, let's say we only download one every two (13,15,17,19).
  3. Download a higher quality version on a higher zoom level, let's say 10 and split it up in the client.

Do any of these sound reasonable? What else could we do?

Thanks a lot!

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3 Answers

up vote 1 down vote accepted

I have never worked with cloudmade, we serve everything in-house, but that's my advice

Here is some input I'd consider in your situation:

  • Try to set PNG256 / PNG8 as de FileFormat instead of PNG (saves about 50%)
  • Start with one of those OSM-minimal stylesheets (reduction in colors, information etc.)

I think it should be doable to get sub 100kb for one full map request on a mobile device (excl. iPad). With the right compression, 8bit colors, minimal style, etc...

Cheers Martin

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What do you mean exactly you serve everything "in-house"? Where do you get the maps from? – frowing Sep 20 '12 at 14:02
We have a server with PostGIS and Mapnik on it. As cache there is a TileCache system running serving the WMS-T maps ready for any device. Maps are made by us inspired by osm-bright - at least the stylesheet. The dataset can be downloaded from download.cloudmade.com, but be aware, it takes atleast 6 months (I had 9) of work to understand and get a system running, if you are a nonGIS head. ;) – Martin Sep 20 '12 at 15:46
up vote 2 down vote

I've never used Cloudmade but generally caching will improve the performance greatly. Did a quick search and it looks like cloudmade prohibits caching of their tiles offline on your own servers unless you have the right API subscription key. Not sure if you have that, but if you don't looks like you will be in violation of their TOS.

http://support.cloudmade.com/mobile-fair-use

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up vote 1 down vote

Use the "multiple simultaneous downloads" which cloudmade servers supports with a valid API KEY

a.tile.cloudmade.com - the server we're getting the image from. We have [abc]-subdomains to allow parallel downloads -

b.tile.cloudmade.com - the server we're getting the image from. We have [abc]-subdomains to allow parallel downloads -

c.tile.cloudmade.com - the server we're getting the image from. We have [abc]-subdomains to allow parallel downloads

http://developers.cloudmade.com/projects/tiles/documents

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