[OSM-talk] mark a way as secondary

[Simon Hewison]

On Sat, Jun 10, 2006 at 01:46:26PM +0200, Thomas Walraet wrote:
> Another big problem to keep in mind for people searching for the best 
> tagging system is the "roundabout problem". A junctions can be road, 
> rail, etc. and it can be primary or not... I like the idea of clearly 
> tagging junctions, because it can help an automatic simplification of 
> maps at higher level.

You don't *need* any tags to get a simple algorithm to find junctions.
You just need to look at any node with more than two segments attached
to it.

For high-level simplification of maps, for instance, for route planning,
all that you really need to know of is how to get from one junction
to another, so the whole concept of segments and ways can almost
be disregarded, you just need to know that to get from node A to node
B, you need to know it's X km in distance, the maximum height is Y metres,
the maximum weight is Z tonnes, and what the restrictions are. With the
current "Map Features" way of doing things, it's trivial to simplify
such a route, and summarize any restrictions. Nor, for that matter do you
need to know that the low bridge is 304 metres down that road, just that
it exists, and is Y metres above the road.

For a route planning software, you don't need to know that there's
a pub 465 metres past the Natwest Bank on the left hand side, nor do you need
to know that that pub serves rather delicious hot salt beef sandwiches
and a selection of cask ales.

Likewise, the "roundabout" problem isn't a problem if you use something
like "junction=roundabout". It doesn't _really_ matter what colour it is
on the map, though cartographer's convention is normally that you colour
a flat junction in the colour of the most major way that meets there.
(grade-separated junctions, like motorway junctions, are normally
rendered differently depending on scale)

--
Simon Hewison