A node is one of the core elements in the OpenStreetMap data model. It consists of a single point in space defined by its latitude, longitude and node id.
A third, optional dimension (altitude) can also be included: key:ele. A node can also be defined as part of a particular layer=* or level=*, where distinct features pass over or under one another; say, at a bridge.
Nodes can be used to define standalone point features, but are more often used to define the shape or "path" of a way.
Over 2 000 000 000 nodes exist in the global OSM data set (as of 2013).
Nodes can be used on their own to define point features. When used in this way, a node will normally have at least one tag to define its purpose. Nodes may have multiple tags and/or be part of a relation. For example, a telephone box may be tagged simply with amenity=telephone, or could also be tagged with operator=*.
Nodes on Ways
- See also: Way
Many nodes form part of one or more ways, defining the shape or "path" of the way.
Where ways intersect at the same altitude, the two ways must share a node (for example, a road junction). If ways cross at different heights, without connecting, they may not share a node (e.g., where a road crosses over a river at a bridge=*). Where ways cross at different heights they should be tagged with different layer=* or level=* values, or be tagged with location=* 'overground' or 'underground'. It can be necessary to split a way on occasions to prevent ways on different layers or levels from meeting at a node.
Some nodes along a way may have tags. For example:
- highway=crossing + crossing=* to define a pedestrian crossing along a highway=*
- natural=tree to identify a lone tree on a barrier=hedge
- building=entrance to identify a doorway into a building=*
|Node ids are unique between nodes. (However, a way or a relation can have the same id number as a node.) Editors may temporarily save node ids as negative to denote ids that haven't yet been saved to the server. Node ids on the server are persistent, meaning that the assigned id of an existing node will remain unchanged each time data are added or corrected. Deleted node ids must not be reused, unless a former node is now undeleted.|
≥ −90.0 and ≤ 90.0
with 7 decimal places
|Latitude coordinate in degrees (North of equator is positive) using the standard WGS84 projection. The precision required is compatible within the supported value range with the 64-bit floating point format defined in the IEEE standard. (The 32-bit format may give 7 significant figures, but not 7 decimal places.) Some applications may not accept latitudes above/below ±85 degrees for some projections.|
≥ −180 and ≤ 180
with 7 decimal places
|Longitude coordinate in degrees (East of Greenwich is positive) using the standard WGS84 projection. The precision required is compatible within the supported value range with the 32-bit floating point format defined in the IEEE standard. Note that the geographic poles will be exactly at latitude ±90 degrees but in that case the longitude will be set to an arbitrary value within this range.|
|tags||A set of key/value pairs, with unique key||See Map Features for tagging guidelines.|
<node id="25496583" lat="51.5173639" lon="-0.140043" version="1" changeset="203496" user="80n" uid="1238" visible="true" timestamp="2007-01-28T11:40:26Z"> <tag k="highway" v="traffic_signals"/> </node>