[Tagging] Bridges redux

Richard Fairhurst richard at systemed.net
Fri May 10 10:24:04 UTC 2013

Christopher Hoess wrote:
> Specifically, what made me switch was thinking about renderers, 
> routers, and other consumers of the data.

OSM's most valuable resource is mappers. We should therefore optimise
tagging schemes for ease of mapping.

I don't think non-programmers realise how easy it actually is to cope with
tag variations, especially now that our tools are so sophisticated. For
renderers, the standard is osm2pgsql+Mapnik/Tilemill: Carto makes it easy to
assemble tagging rules, and osm2pgsql has (just!) got lua-based tag
transformations. For routers, the standard is OSRM, and that too has
lua-based tag transformations.

I'm currently working on two rendering projects (one for bikes, one for
boats) and one routing project (for bikes). Even coping with paths, the most
complex tagging scheme that we have, is really easy with the lua+Carto
combination; just 20 lines of code sorts out the complexities of access=,
bicycle=, designation=, highway=, tracktype=, and surface= into the three
rendering categories I want. 

So for the tiny number of renderers/routers which want to show bridge types
differently - and my canal renderer will be one of them! - differentiating
based on a single bridge= tag is plenty easy enough. For the majority of
renderers/routers, "it's a bridge" will suffice.

The simplicity and reduced burden for mappers wins out, as indeed it should
always do. And I'm looking forward to people tagging more swing bridges and
lift bridges so I can make a nice canal map. :)


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