[OSM-dev] Can we have higher resolution tiles?

[Andy Allan]

On Wed, Jun 15, 2011 at 1:23 PM, Parveen Arora <osm at parveenarora.in> wrote:
> On Wed, Jun 15, 2011 at 10:10 AM, Graham Jones <grahamjones139 at gmail.com> wrote:
>> Hi Parveen,
>> Do you mean resolution (pixels per inch) or level of detail (which icons
>> appear at which zoom level?).
> Yes I meant to pixels per inch.
>
>> You can change the resolution if you use mapnik2, but that is something you
>> would want to do for printed output rarher than a web based map?
> Yes, someone asked me to print them for his area, but one I printed is
> not of good quality.
> So I wants to increase the resolution of tiles for local OSM Tile Server.

OK, so it's impossible to change the resolution of images, since they
don't have a resolution. Images only have a number of pixels, that's
it.

When stuff is shown on screen it's usually shown around 90 pixels per
inch. Most times when you print a webpage then it'll assume that you
still want to print at 90 pixels per inch, regardless of the DPI of
the printer. In order to look crisp, you want to find a way to
instruct your printer to print at more pixels per inch, say 250 pixels
per inch. Again, don't confuse this with the DPI setting of the
printer, since that's about number of ink droplets on the page, and
not to do with pixels per inch.

Now to make things like the width of a road or icon of a church stay
at the same size, you would need to increase the number of pixels they
are measured in. So a road would need to be e.g. 15 pixels instead of
5. That usually involves changing the stylesheets, although there is
work on this going on in mapnik2 to allow this to be controlled
without editing the stylesheet.

You could have a look at the "oversize" tiles that CloudMade produce.
http://developers.cloudmade.com/projects/tiles/documents . You can see
in the second example everything is drawn bigger, so that if you were
to print out at 180 pixels per inch it would look the same size as a
normal map, but you'll end up with a better looking map.

Finally, if you are printing it's often worth ignoring all this stuff
and just printing from SVG. You can get SVG output from the Export
tab.

Cheers,
Andy