[mkgmap-dev] resolution, level & levels

Thu Sep 13 11:53:42 BST 2012

I'm confused about the way resolution, level and levels interact.

I started with a set of supplied styles (actually from Marco Certelli's 
CreateIMG package) which used resolutions 14, 16, 18, 20, 22 & 24 for 
various kinds of roads. I wanted to change residential roads to come 
higher than tertiary roads (resolution=22) but lower than footways & 
tracks (resolution=24), so I changed them to be at resolution=23. 
Unfortunately this didn't work -- they appeared and disappeared at the 
same time as the the resolution=22 tertiary roads.

I then changed the levels specification from the supplied

  levels = 0:24, 1:22, 2:20, 3:18, 4:16

to

  levels = 0:24, 1:23, 2:22, 3:20, 4:18, 5:16

and everything sprang into life working as desired. This behaviour was 
consistent between BaseCamp and my Oregon.

The documentation in

  http://wiki.openstreetmap.org/wiki/Mkgmap/help/style_rules

had led me to think (though I guess it doesn't say so explicitly) that 
level & levels were meaningful only to the Mkgmap compiler, and were 
converted to resolution in the final Garmin format map files. As a result 
I was surprised that changing the levels specification had any effect at 
all, since all rules used resolution rather than level anyway.

Could anyone shed any light on this behaviour? Thanks!

-- 
Cheers,
John