I have a query regarding the above mentioned. I have a river and a footpath at low level bridged over by a light railway and cycle path.
The questions are do all the four crossing points need nodes?
The cycle path and light railway are side by side over the footpath and river, how do I make one bridge including the cycle path and railway?
On a similar vein in another instance I have an existing mapped railway under which I wish to map a footpath. Question is how can I map the footpath as under the railway? I am familiar with mapping bridges but making one way go under another has fooled me.
On a lighter note there’s a heck of a lot to learn to map correctly and I seem to only be able to learn the correct way by making a lot of mistakes. Persistence is paying off though and I’m happy with what I’ve achieved so far.
If I understand your question correctly, NONE of the crossing points needs nodes. You have four ways, the river and footpath at one level, the light railway and cycle path at a higher level. None of these ways joins one of the others, they do not intersect. Therefore there is no need to have any shared or co-located nodes. Take a look here at an identical topology http://osm.org/go/eu8ZePvU9– (Nottingham Tram crossing the River Leen). The two higher level ways have simply been tagged bridge=yes and layer=1.
There is an option to use a relation for the bridge. This is fairly extensively used (over 1500 uses), but is not rendered and is quite complex to tag. See http://wiki.openstreetmap.org/wiki/Relations/Proposed/Bridges_and_Tunnels. Personally, I just note when ways share a bridge, and keep to the simple tagging scheme. I then have to put up with less than ideal renders (particularly bad when a dual carriageway has distinct cycleways and footpaths), but at least I can see that they are bridges.
Just map the footpath as you would normally. Then use the layer tag to show that the railway and footpath are separated in height. It is usual to put the layer tag on the bridge. If, for whatever reason, you want it on the footpath, then cut the footpath way before and after the bridge and add layer=-1 to the small section under the railway bridge. This latter approach is more usually used for footpaths running through a subway. In the on-line editor (Potlatch) the ‘x’ key will cut a way at the selected node.
I think we all learn that way. It’s still worth spending time looking at an area which you know which has been thoroughly mapped to see how others do it. It’s also no problem to ask here or on IRC, talk-gb for someone to have a look at your mapping and over more advice. It is always helpful to provide a link to the slippy map of the area under discussion.