Node
A node is one of the core elements in the OpenStreetMap data model. It consists of a single geospatial point using a latitude and longitude. A third optional dimension, altitude, can be recorded; key:ele and a node can also be defined at a particular layer=* or level=*. Nodes can be used to define standalone point features or be used to define the path of a way.
Contents |
Point features
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 it's purpose or be part of a Relation and may have multiple tags. For example a telephone box may be tagged simply with amenity=telephone but may also be tagged with operator=*.
As part of one or more ways
- See also: Way
Nodes forming part of one or more ways to define the path of the way. Where ways cross at the same vertical location the ways should share a node (for example a road junction); where way cross at different vertical heights they should not share a node. (for example where a road crosses a river with a bridge=*). Where ways cross at different heights they should be tagged with different layer=* or level=* values or be tagged with location=* or 'overground' or 'underground'.
Some nodes along a way can 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 an entrance into a building=*
If two ways meet at the same point in space they should share a node, if they do not then they shouldn't. For example a side road meeting a main road at a junction should share a note, however a road crossing a river should not. Where ways meet at a node the ways should be at the same level=* and layer=* if this is defined for the ways. It may be necessary to split a way on occasions to avoid ways on different layers or levels meeting at a node.
Structure
| name | value | description |
|---|---|---|
| id | integer >= 1 |
Node id's are unique only between nodes. (A way can have the same id. as a node.) Editors tend to save these as negative to denote id's that haven't been saved to the server. Node ids on the server are persistent meaning that the assigned id of an existing node will remain unchanged when data is added or corrected. Deleted node id's must not be reused, unless if the same node is undeleted. |
| lat | float >= −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 32-bit floating point format defined in the IEEE standard. Some applications may not accept latitudes above/below ±85 degrees for some projections. |
| lon | float >= −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. |
Example
<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>
