Very big +1 for that.
Moving from implicit tagging to explicit tagging would cause the size of
the database to explode. An alternative approach may be to have an
optimised function available to derive the "jurisdiction" or "territory"
from specific admin boundaries, and hang the territory-specific defaults
off of them somehow. I can imagine that the admin level will vary by
country; in a federal state such as the USA or Germany there may be
rules set at both a central level and a state level, but the number of
states involved is probably low enough to only do it at a state level
and copy the national defaults down to the states where they may be
overridden. This will avoid needing a hierarchy of jurisdictions. As
there are (IIRC) about 250 countries in the world, and the majority are
non-federal for these purposes, there might be perhaps 500 territories
involved, each being a multipolygon with maybe 0.5kb of data for each
giving about 250kb of attribute data for the territory lookup.The
polygon data will be quite a bit bigger of course. On the face of it, it
sounds as though it might be doable.
Colin
On 26/08/2010 13:26, Ian Spencer wrote:
Craig Wallace wrote on 25/08/2010 22:28:
On Wed, 25 Aug 2010 20:41 +0100, "Ian Spencer"<[email protected]>
wrote:
I think "already by definition cycle-legal" is the very point I
am querying. The trouble with the Bicycle restrictions section is
that it falls at the first hurdle as nobody seems to have defined
(on an international basis remember) whether the use of trunk
implies bicycle=yes or no. I wouldn't want to cycle on the A42
(perceived as a motorway), I have cycled along dual carriageways
around Redditch which are the same in OSM but quite different in
quality. The problems of an administrative definition rather than
a "on the ground" definition even though unless there is explicit
sign-age there is a legal right.
This page defines the default access tags for each highway type in a
number of countries:
http://wiki.openstreetmap.org/wiki/OSM_tags_for_routing/Access-Restrictions
Though its currently lacking a section for the UK. I think the UK should
be much the same as the global defaults, at least for the roads.
The paths/bridleways/cycleways should be a bit different from the
defaults, as access on foot is usually allowed on all of these. It
should probably also be different for Scotland vs England& Wales etc
due to the rather different the access laws.
Though I don't know if there is any maps / routing software using these
defined defaults anyway.
Also, i think there are a few roads in the UK where cycling is banned,
but they haven't been tagged as such (eg parts of the Edinburgh
bypass?).
I think it would be helpful if something like OpenCycleMap highlighted
roads tagged with bicycle=no - it would make the missing bits more
obvious, and might encourage people to map more of them.
Craig
If there are defaults defined with the authority of the project behind
it, then Mr Velo or other people deriving software from the project
would have something to abide by and would have to put function in to
deal with it. When it is undefined, there is not a sensible discussion
to have. However, I could point Mr Velo to the variations that are
defined which would then mean that he could implement a system for
routing appropriately by country.
However, if we consider the change across a European border (my
geography is challenged, but picking an example I saw, Turkey has a
definition that defined trunk roads as defaulting to cycle accessible
and Germany has an override that trunk roads are not accessible, with
a global default that trunk roads are accessible). If we pretended
that Germany had a border with Turkey (pretend I am an American for
European geographical purposes!) then how would the programmer using
OSM data know what country a road was in?
In Velomap's case, he is taking what he knows of how Garmin routing
software works and altering the characteristics of the generated maps
based on tags in OSM to the attributes of the routes in the Garmin.
The Garmin does not understand country borders, the attributes are
assumed to be set. So the Velomap translation would have to understand
what country any way was in to work out what the OSM attributes really
are so they can be mapped appropriately to Garmin. More generally,
every routing software based on OSM needs to understand how to map the
tags to known routing attributes, and as it stands it is not well
defined and means that currently no software based on OSM source can
be properly designed to work internationally.
It would be easy to amend the editors to always apply default tags for
cycling, walking and other issues and allow the editor to set these
values depending on circumstance (or allow e.g. potlatch to have
country configuration to apply appropriate defaults). The presumption
of defaults (e.g. highway=foot might or might not mean "public
footpath" in the legal sense) means that the data in OSM is unsound.
If I were designing a database for business use I'd want any such
presumption defined in stone if I was writing software that relied on
it - either these things should be bottomed out, or they should not be
relied on and everything should be explicitly tagged.
Spenny
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