[OSM-newbies] layer essentials

[Ed Loach]

Robert asked:

> Also, does adding a bridge section with a layer of 1 mean 
> I should also tag the surface road with a layer of 0 or 
> is the default no tag (layer 0) good enough?

I think no tag of layer 0 is good enough. I only add layer=1
(usually; occasionally 2 on complicated junctions) to the bridge,
and don't tag the layer 0 way(s).

See
http://wiki.openstreetmap.org/index.php/Key:layer
and
http://wiki.openstreetmap.org/index.php/Key:bridge

Having said that, some tags assume certain layers I believe. I think
for example landuse=<whatever> renders (at least in Osmarender) as
layer -5 to be behind everything else. 

I'm sure I read somewhere that water features such as rivers and
streams should be kept at layer 0 and any crossing ways then be set
appropriately (something about water can't flow uphill to a higher
layer), but I can't find that reference now. 

Ed