[OSM-talk] Road cores and casings on standard Mapnik rendering

Frederik Ramm frederik at remote.org
Fri Jan 20 08:16:17 GMT 2012


     I'm copying this message over from help.openstreetmap.org 
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.



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)







 From this I have extracted estimations the core-casing values and put 
them here:


(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: 

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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