                                OpenStreetMap Tagging
                                =====================

   The different tags that are used by the router software are described
   below.

Node Tags

   The only node tags that are used are the id, latitude and longitude of
   the node. The id tag is required to associate the node with the ways
   and the position tags are not tags in the normal sense.

Way Tags

   The tags from the ways in the data are the ones that provide most of
   the information. The tag is used only so that the segments can be
   associated with a way.

The highway Tag

   The most important tag that is used from a way is the highway tag. This
   defines the type of highway that the way represents. Any way that does
   not have a highway tag is discarded.

   There are more highway types defined than are used by the router. The
   subset that the router uses are:
     * Motorway
     * Trunk
     * Primary
     * Secondary
     * tertiary
     * unclassified
     * residential
     * service
     * track
     * path
     * bridleway
     * cycleway
     * footway

   The other highway types are assumed to be equivalent to one of the
   types listed above according to the table below.

                        Highway type  Equivalent type
                            byway          track
                        living_street   residential
                            minor      unclassified
                         pedestrian       footway
                            road       unclassified
                          services        service
                            steps         footway
                         unsurfaced        track
                           unpaved         track
                           walkway        footway
                CAPTION: Aliasing of equivalent highway types

   The second important thing that can be taken from the highway tag is
   the type of tansport that is allowed to use the highway. The list can
   be modified depending on other tags, but the default assumptions are as
   shown in the table below.

     Highway    foot bicycle horse motorbike motorcar goods hgv psv
   motorway     no   no      no    yes       yes      yes   yes yes
   trunk        yes  no      no    yes       yes      yes   yes yes
   primary      yes  yes     yes   yes       yes      yes   yes yes
   secondary    yes  yes     yes   yes       yes      yes   yes yes
   tertiary     yes  yes     yes   yes       yes      yes   yes yes
   unclassified yes  yes     yes   yes       yes      yes   yes yes
   residential  yes  yes     yes   yes       yes      yes   yes yes
   service      yes  yes     yes   yes       yes      yes   yes yes
   track        yes  yes     yes   no        no       no    no  no
   path         yes  yes     yes   no        no       no    no  no
   bridleway    yes  yes     yes   no        no       no    no  no
   cycleway     yes  yes     no    no        no       no    no  no
   footway      yes  no      no    no        no       no    no  no

   CAPTION: Default assumption about allowed transport on different
   highway types

   The type of highway and the method of transport chosen for routing
   together define a default maximum speed limit.


   One additional assumption is that a motorway implies that the highway
   is also oneway.

The access Tag

   The access tag is used to specify the default access restrictions on
   the way.

   If the access tag is set to one of the values true, yes, 1, permissive
   or designated then the normal access permissions above apply. If the
   access tag is set to any other value then the default setting for the
   way is set to no types of transport.

   In addition to the access tag there is also one tag for each of the
   different modes of transport: foot, bicycle, horse, motorbike,
   motorcar, goods, hgv and psv. If one of these tags is present and the
   value is set to one of true, yes, 1, permissive or designated then that
   particular transport type is allowed (even if the generic access tag
   says that it is not). If the tag is present but not one of the values
   above then it is assumed that the particular form of transport is
   forbidden.

   For example a highway that has the tags: highway=service,
   service=driveway, access=private, foot=designated is a private driveway
   that has a public footpath running along it (not uncommon in the UK).

The name Tag

   The name tag is used to provide the label for the highway when printing
   the results.

The ref Tag

   The ref tag is used to provide the label for the highway when printing
   the results.

The junction Tag

   The junction tag is used only to check if a highway is (part of) a
   roundabout. This tag is used for information to label the highway if no
   other name is provided.

   In addition to providing the label for the highway the presence of the
   junction=roundabout tag also implies the highway is oneway.

The oneway Tag

   The oneway tag is used to specify that traffic is only allowed to
   travel in one direction. When tagging it is important to make sure that
   the direction that traffic is allowed follows the order of the nodes in
   the way.

The maxspeed Tag

   The maxspeed tag is used to specify the maximum speed limit on the
   highway. This is always measured in km/hr in OpenStreetMap data (some
   attempts are made to detect a tag that contains "mph" and convert it).

The maxweight Tag

   The maxweight tag is used to specify the maximum weight of any traffic
   on the way. In other words this must be set to the heaviest weight
   allowed on the way (for example a bridge) in tonnes.

The maxheight Tag

   The maxheight tag is used to specify the maximum height of any traffic
   on the way. In other words this must be set to the lowest height of
   anything above the way (like a bridge) in metres.

The maxwidth Tag

   The maxwidth tag is used to specify the maximum width of any traffic on
   the way. This must be set to the minimum width of the contraints at the
   wayside in metres.

The maxlength Tag

   The maxlength tag is used to specify the maximum length of any traffic
   on the way (usually from a traffic sign) in metres.

Relation Tags

   Currently no relation tags are used.


--------

Copyright 2008,2009 Andrew M. Bishop.
