[OSM-talk] [tagging] Feature Proposal - RFC - Clearance

[Roy Wallace]

On Fri, Jul 31, 2009 at 11:04 AM, John Smith<delta_foxtrot at yahoo.com> wrote:
> How much does the physical height exceed the legal height in most cases?

This is difficult to answer. For a way passing under a bridge, I would
argue the limitation is (semantically) a physical one and not a legal
one.

> If maxheight already implies the legal height there is no need to make things convulted for the sake of it, otherwise we'd be typing denomination=the_church_of_jesus_christ_of_latter-day_saints

The maxheight documentation does not make such an implication.

> If the bridge has a horizontal bottom and the way underneath is flat most of the time the legal and physical maximums will be about 15cm different, breathing room if you like.
> However if the above criteria isn't met the physical difference will vary, say the way dips underneath it wouldn't be the same as the entry or exit from under the obstruction. Or the previous example of one side the lane being different to the other, this won't help trucks as they can't make themselves the same size as unicyclists.

What about a way that has either a physical limitation or a legal
limitation (not both). Perhaps there is some argument that the tag
should differentiate between these situations? Though I admit I can
only think of a weak one - that it makes it clearer for users and
mappers - e.g. seeing that a way has been tagged with
maxheight:physical might implies that it relates to the crossing
bridge, whereas if it was tagged with maxheight:legal, it would be
worth my while to go out and check the clearance signage on the
bridge...