170 lines
6.2 KiB
ReStructuredText
170 lines
6.2 KiB
ReStructuredText
Relations
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=========
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In `OpenStreetMap, relations <http://wiki.openstreetmap.org/wiki/Relation>`_ define logical or geographic relationships between other nodes, ways and relations.
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The most common relation type is a multipolygon, but all other relations can be imported as well.
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Multipolygons
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-------------
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`Multipolygon relations <http://wiki.openstreetmap.org/wiki/Relation:multipolygon>`_ are used to represent complex polygon geometries. They are also the only way to represent holes in polygons.
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Multipolygon relations are automatically handled by Imposm for all ``polygon`` tables.
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The following mapping::
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tables:
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buildings:
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type: polygon
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mapping:
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building: [__any__]
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Inserts closed ways if they have a ``building`` tag::
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<way id="1001" version="1" timestamp="2011-11-11T00:11:11Z">
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<nd ref="1001"/>
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...
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<nd ref="1001"/>
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<tag k="building" v="yes"/>
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</way>
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It will also insert relations of the type ``multipolygon`` with a ``building`` tag::
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<relation id="17101" version="1" timestamp="2011-11-11T00:11:11Z">
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<member type="way" ref="17101" role="outer"/>
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<member type="way" ref="17102" role="outer"/>
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<tag k="type" v="multipolygon"/>
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<tag k="building" v="yes"/>
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</relation>
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The roles are ignored by Imposm as not all holes are correctly tagged as ``inner``. Imposm uses geometry operations to verify if a member of a multipolygon is a hole, or if it is a separate polygon.
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Old-style multipolygon relations with tags on the outer way, instead of the relation are no longer supported.
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Other relations
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---------------
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OpenStreetMap also uses relations to map more complex features. Some examples:
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- `Administrative areas <http://wiki.openstreetmap.org/wiki/Relation:boundary>`_ with boundaries, capitals and label positions.
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- `Bus/tram/train routes <http://wiki.openstreetmap.org/wiki/Relation:route>`_ with the route itself, stops and platforms.
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- `3D buildings <http://wiki.openstreetmap.org/wiki/Simple_3D_buildings>`_ with multiple parts that should not be computed as holes.
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These relations can not be mapped to `simple` linestrings or polygons as they can contain a mix of different geometry types, or would result in invalid geometries (overlapping polygons).
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The Imposm table types ``relation`` and ``relation_member`` allow you to import all relevant data for these relations.
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``relation_member``
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^^^^^^^^^^^^^^^^^^^
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The ``relation_member`` table type inserts each member of the relation as a separate row. The ``relation_member`` has access to the `role` and `type` value of each member. You can also import tags from the relation `and` from the member node, way or relation.
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Example
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~~~~~~~
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You can use the following mapping::
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route_members:
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type: relation_member
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columns:
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- name: osm_id
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type: id
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- name: member
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type: member_id
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- name: index
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type: member_index
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- name: role
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type: member_role
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- name: type
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type: member_type
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- name: geometry
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type: geometry
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- name: relname
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key: name
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type: string
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- name: name
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key: name
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type: string
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from_member: true
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- key: ref
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name: ref
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type: string
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relation_types: [route]
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mapping:
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route: [bus]
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to import a bus relation with stops, a platform and the route itself::
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<relation id="100901" version="1" timestamp="2015-06-02T04:13:19Z">
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<member type="node" ref="100101" role="stop_entry_only"/>
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<member type="node" ref="100102" role="stop"/>
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<member type="way" ref="100511" role="platform"/>
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<member type="node" ref="100103" role="stop_exit_only"/>
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<member type="way" ref="100501" role=""/>
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<member type="way" ref="100502" role=""/>
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<member type="way" ref="100503" role=""/>
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<tag k="name" v="Bus 301: A => B"/>
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<tag k="network" v="ABC"/>
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<tag k="ref" v="301"/>
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<tag k="route" v="bus"/>
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<tag k="type" v="route"/>
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</relation>
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This will result in seven rows with the following columns:
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======== ======================================================================================================================================================
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Column Description
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======== ======================================================================================================================================================
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osm_id The ID of the relation. 100901 for all members.
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member The ID of the member. 100101, 100102, etc.
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index The index of the member. From 1 for 100101 to 7 for 100503. This can be used to query the bus stops in the correct order.
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role The role of the member. ``stop``, ``platform``, etc.
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type 0 for nodes, 1 for ways and 2 for other relations.
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geometry The geometry of the member. Point for nodes and linestring for ways.
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relname The value of the ``name`` tag of the relation. ``Bus 301: A => B`` in this case.
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name The value of the ``name`` tag of the member element, if it has one. Note that the mapping contains ``from_member: true`` for this column.
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ref The value of the ``ref`` tag of the relation. ``301`` in this case.
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======== ======================================================================================================================================================
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You can insert the tags of the relation in a separate ``relation`` table to avoid duplication and then use `joins` when querying the data.
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Both ``osm_id`` and ``member_id`` columns are indexed in PostgreSQL by default to speed up these joins.
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``relation``
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^^^^^^^^^^^^
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The ``relation`` table type inserts the mapped element regardless of the resulting geometry. For example, this allows you to create a table with the metadata (name, reference, operator, etc.) of all available route relations. The actual geometries need to be `joined` from the members.
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Example
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~~~~~~~
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The following mapping imports the bus route relation from above::
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routes:
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type: relation
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columns:
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- name: osm_id
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type: id
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- key: ref
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name: ref
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type: string
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- name: network
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key: network
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type: string
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relation_types: [route]
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mapping:
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route: [bus]
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This will create a single row with the mapped columns.
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.. note:: ``relation`` tables do not support geometry columns. Use the geometries of the members, or use a ``polygon`` table if your relations contain multipolygons.
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