[mkgmap-dev] [PATCH] reduce highway=service resolution

Tue Aug 11 14:33:53 BST 2009

On Mon, Aug 10, 2009 at 09:14:59PM +0200, Ondrej Novy wrote:
> It think we should set resolution for residential streets back to 21, now is
> map just 'empty'.

I don't know.  I don't have a car and am using a bicycle for most of my
transportation needs (routinely up to 20 km one way, sometimes even 100 km
per day).  I sometimes prefer to ride through residential streets, if the
cycleways along major roads are badly constructed.  But I would assume that
motorists don't want to see residential streets when navigating longer
journeys.

If I use routing, which generally works nicely on the Edge 705, I will
see the pink line also on low zoom levels where the streets themselves
would be invisible.  The map on low zoom levels would update quicker if
it didn't show residential streets.  If I need to see the residential
streets, I will switch to 50 or even 20 meter zoom level, no problem.

I think that the resolution should depend on the context.  For example,
I think that cycleways, paths or tracks running aside a bigger road should
be suppressed on low zoom levels.  But if they are the only road in the
area, then they should be displayed.  The same applies to residential roads,
of course.  In some places, the only route through an area is a residential
road that goes through a village.

How to reliably detect this, I don't know.  If there is a highway=cycleway
running next to a car highway, then there should be several crossings,
bridges or tunnels between the ways.  Maybe it would be enough to calculate
the average distance between the ways, and omit the lesser way on lower zoom
levels if it is "parallel" to the more important road.  Or maybe just omit
the "parallel" section of the lesser road, e.g., if the cycleway includes a
"ramp" to another road, like this:

  |
==*======== highway={unclassified,residential,tertiary,secondary,primary}
  |  ------ cycleway or footway
  | /
  |/
  ||

In this case, the vertical and horizontal sections of the cycleway could
be omitted at low zoom levels.

> If we want to have this set to resolution 23 we need to update more than
> just service, but parking and track for example too.

Could we perhaps define a partial order of elements that a test case could
check, to prevent similar inconsistencies in the future?  E.g., check that
the following holds in the style file:

resolution(highway=secondary) <= resolution(highway=primary)
resolution(highway=tertiary) <= resolution(highway=secondary)
...

> So i'm voting to set residential back to 21 :].

I'm fine either way.

	Marko