[mkgmap-dev] Fun with splitter tile descriptions

Fri Sep 11 22:05:02 BST 2009

Thanks Johann, this sounds like quite a reasonable approach too. It shouldn't 
be too hard to add in to the splitter (eg by tacking the info on to the density 
map, or by holding on to the is_in data until the areas are known then calculating 
the names as a separate step). Looking at a few osm files the is_in tags 
and their values seem inconsistent at best though so I don't know how easy 
it would be to get sensible/consistent data from them. Another possible issue 
is that osm files without the tags wouldn't work at all. If you do have some 
code that deals with filtering/sanitising the is_in data I'd be interested 
to see it however as it sounds like it would be worth investigating further.

The approach I'm currently looking at is using a geonames file (eg cities15000.zip) 
from http://download.geonames.org/export/dump/ to decide which country and 
city is the most predominant one in each tile. The advantage is it should 
be very fast and accurate, won't require an internet connection (aside from 
the initial download of the file), and can be tailored by people if they 
use custom input files. The downside is the minor hassle involved in dealing 
with that extra file. Depending on how well this approach works in practice 
and what feedback I get, I might look at making the automatic tile naming 
more configurable/plugable at a later date.

Chris

JG> I played with an similar thing some time ago, a year or so. My
JG> algorithm was not searching for the biggest city, but counted the
JG> 'is_in' tags of the osm data. The idea behind it was that should
JG> scale with different resolutions. With big tiles it should name the
JG> tiles with the names of boundaries, if I break it down into small
JG> tiles it should take the names of the cities and villages. With
JG> statistical probability in a big city exists much more is_in tags as
JG> in a small village.
JG> 
JG> This was inedependent of the geonames service and fully based on the
JG> osm data.
JG> 
JG> As far as I can remind, the results worked in general, but the code
JG> does not fit well into the splitter. I would have to search on my
JG> harddrive, if the code lays around somewhere.
JG> 
JG> Regards,
JG> Johann
JG> Clinton Gladstone schrieb: