What kind of improvement can be done for raster tiles for mobile usage

Question

We generate raster map tiles and deploy them in the server, then we use javascript in the client to request the tiles and re-organize them to map.(like google map and Openstreetmap).

However this is the PC solution. And the tile size is 256x256(pixel) with 96dpi.

Now we want to build apps in android and iOS.

However we found that the same 256x256(pixel) tile will have a different visual effect in devices with different resolution and the tile is almost unreadable in a high-resolution device(The text and labels in the tile is too small).

Then I wonder how do you make the tiles readable in the mobile device, is there any way to improve them?

Answer 1

I think the only way is to rerender the map for a bigger ppi device, and serve that on mobile devices. Rerender would include bigger labels, larger symbols, etc.

Answer 2

Openlayers allows you to change the DPI setting using something like:

OpenLayers.DOTS_PER_INCH = 96;

Of course, you'll still need to increase the DPI on your tile-server; no idea how to do that as we don't know what you're using.

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The "correct" answer however is likely a non-technical one.

You need to design your tiles for the target audience as you would with any map. Read the Ordnance Survey's Cartographic design principles - You'll see there's a section for Consideration of display format. What you need to do is redesign your tiles so they're better suited for the mobile displays you're targeting. I suspect that one carefully designed style would work for both PC and mobile.

Answer 3

I've had good luck with pulling mbtiles from MapBox onto Android devices. Perhaps you might want to serve tiles with TileStream.