Hi,
I'm copying this message over from help.openstreetmap.org
(http://help.openstreetmap.org/questions/10088/mapnik-rendering-road-cores-and-casings)
which is unsuitable for discussions. It is written by user "Ben", and I
have closed the question on help and requested a move to the mailing list.
------------------------------------------
Hi,
In short I'm wondering if someone would be able to have a look at the
mapnik rule sheet on road widths, in regards to what I shall elaborate
on. I have done about as much as I am able to do myself.
On the Mapnik renders there are a few differences in the road widths
which I would like to propose getting a bit of a tweaking. I haven't
looked at the rulesheet itself for a couple of reasons, so I started by
making a test area for the different zoom levels for the road
combinations. (excluding _link being down the central line).
(all these links are having the underscore dropped before the last -
because it seems to be the italic shortcut)
http://wiki.openstreetmap.org/w/images/1/14/Core-Casing_-Z13.png
http://wiki.openstreetmap.org/w/images/0/02/Core-Casing-Z14.png
http://wiki.openstreetmap.org/w/images/2/21/Core-Casing-Z15.png
http://wiki.openstreetmap.org/w/images/e/e5/Core-Casing-Z16.png
http://wiki.openstreetmap.org/w/images/5/55/Core-Casing-Z17.png
http://wiki.openstreetmap.org/w/images/4/40/Core-Casing-_Z18.png
From this I have extracted estimations the core-casing values and put
them here:
http://wiki.openstreetmap.org/wiki/User:Ben./MapnikRoads
(These are estimates, so may not always be correct, but it makes it
clear where the differences are)
So then I stuck them into this table:
http://wiki.openstreetmap.org/w/images/0/02/Difference_in_Core-Casing.PNG
To evaluate:
The "motorway" and "motorway_link_" are the strangest as they are
smaller than all but a few roads of lower status than them. Then from
trunk to Secondary the roads are a fraction bigger than others, but more
noticeable the casing is thinner. Thirdly the way they increase over
zoom levels isn't smooth at times. Finally the order in which they
render has links render very early, rather than just before there
similarly named road (i.e. motorway_link to motorway).
The main issue with this is in flyover junctions where roads don't flow
nicely into one another; but there are other reasons also.
In conclusion: The answer to this is a bit opinionated so there isn't
really one, but the suggestion I would make is that either all roads bar
maybe residential and service should be the same size with the same
casing, maybe oneday having lanes= taken into consideration. Another
option is to have all roads under and including tertiary as the same
along with all _link roads being the same. Then all roads at secondary
and above levels being steped up bigger. This section would be good to
discuss though for the better idea.
cheers, Ben
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