[OSM-talk] Green areas

[Simon Hewison]

Andy Robinson wrote:
> matthew-osm at newtoncomputing.co.uk [mailto:matthew-
>> osm at newtoncomputing.co.uk] wrote:
>> Sent: 21 September 2006 12:35 PM
>> To: Andy Robinson
>> Cc: 'Joerg Ostertag (OSM Munich/Germany)'; talk at openstreetmap.org
>> Subject: Re: [OSM-talk] Green areas
>>
>> On Thu, Sep 21, 2006 at 12:01:59PM +0100, Andy Robinson wrote:
>>> Agreed, using the elevation key from Map_Freatures is perhaps confusing.
>> In
>>> hindsight I agree, change to "layer" OR "display_layer"
>> For this purpose, yes.
>>
>> For reasons of the "elevation" tag still being used, think M6 J6
>> ("spaghetti
>> junction"). "Bridge" alone is not enough.
>>
>> However, I can not currently see the need to keep the "bridge" tag;
>> "elevation=1" seems equivalent (or elevation=-1 on the underlying way).

elevation implies that one segment lies above another one. It doesn't imply 
HOW that happens, whether it's by bridge, swing bridge, lifting bridge, 
suspension bridge, underpass, tunnel. Maybe someone would be interested in 
what sort of civil engineering is used to achieve the elevated way.

(I thought it was originally "elevated" in the days before "Map Features", 
not elevation, since elevation implies elevation above mean sea level)

If you look at an Ordnance Survey map (and put it away before you start 
copying it), you will see that they render bridges differently to tunnels, 
and multi-level motorway interchanges are quite complicated, because they 
also include cuttings and embankments.
	
Looking around Google Earth the other day, someone's been busy finding 
multi-level intersections, labelling things as "a road above a railway above 
a canal above a road", or suchlike.

-- 
Simon Hewison