A way is an ordered list of nodes which normally also has at least one tag or is included within a Relation. A way can have between 2 and 2,000 nodes, although it's possible that faulty ways with zero or a single node exist. A way can be open or closed. A closed way is one whose last node on the way is also the first on that way. A closed way may be interpreted either as a closed polyline, or an area, or both.
Over 416 000 000 ways exist in the global OSM data set (as of June 2017).
Types of way
An open way is way describing a linear feature which does not share a first and last node. Many roads, streams and railway lines are open ways. Identifying the direction of a 'way'.
A closed way is a way where the last node of the way is shared with the first node with suitable tagging. A closed way that also has a area=yes tag should be interpreted as an area (but the tag is not required most of the time, see section below).
The following closed way would be interpreted as closed polylines:
- highway=* Closed ways are used to define roundabouts and circular walks
- barrier=* Closed ways are used to define barriers, such as hedges and walls, that go completely round a property.
Main article: Area
An area (also polygon) is an enclosed filled area of territory defined as a closed way. Most closed ways are considered to be areas even without an area=yes tag (see above for some exceptions). Examples of areas defined as closed ways include:
For tags which can be used to define closed polylines it is necessary to also add an area=yes if an area is desired. Examples include:
Combined closed-polyline and area
It is possible for a closed way to be tagged in a way that it should be interpreted both as a closed-polylines and also as an area.
For example, a closed way defining a roundabout surrounding a grassy area might be tagged simultaneously as :
- highway=primary + junction=roundabout, both being interpreted as a polyline along the closed way, and
- landuse=grass, interpreted on the area enclosed by the way.
Street as a vector
<way id="5090250" visible="true" timestamp="2009-01-19T19:07:25Z" version="8" changeset="816806" user="Blumpsy" uid="64226"> <nd ref="822403"/> <nd ref="21533912"/> <nd ref="821601"/> <nd ref="21533910"/> <nd ref="135791608"/> <nd ref="333725784"/> <nd ref="333725781"/> <nd ref="333725774"/> <nd ref="333725776"/> <nd ref="823771"/> <tag k="highway" v="residential"/> <tag k="name" v="Clipstone Street"/> <tag k="oneway" v="yes"/> </way>
The nodes defining the geometry of the way are enumerated in the correct order, and indicated only by reference using their unique identifier. These nodes must have been already defined separately with their coordinates.