wiki:Help/Concepts/Object

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Objects - The basic building blocks of OSM data and maps

JOSM helps you to enter data about real-world objects in the OSM geo-database. Despite the overwhelming complexity of real-world objects you can map, JOSM provides only three kinds of objects as basic building blocks for maps: source:trunk/images/data/node.png nodes, source:trunk/images/data/way.png ways and source:trunk/images/data/relation.png relations.

You can assign tags to objects. It's the assigned set of tags which makes a node representing a restaurant different from a node representing a church, or a way representing a residential road different from a ways representing a river, or a relation representing a bus route different from a relation representing a cycling route.

Table of Contents

  1. Nodes, ways, and relations
    1. Nodes
    2. Ways
      1. Closed Ways (Areas)
    3. Relations
      1. Simple explanation
        1. type=multipolygon
        2. type=route
        3. type=restriction
  2. Tags
  3. Object ids
  4. Object versions

Nodes, ways, and relations

Nodes

source:trunk/images/data/node.png A node is an individual point with a defined position.

Ways

source:trunk/images/data/way.png A way is a sequence of nodes. Despite its name a way doesn't represent ways in the real-world only. An OSM way is also used to represent a river, the boundaries of a country, or even a building.

Closed Ways (Areas)

source:trunk/images/data/closedway.png If a way is closed, i.e. if the last node is the same as the first node, it is also called an area.

Relations

Simple explanation

source:trunk/images/data/relation.png A relation is an sequence of other nodes and ways. Every relation can have their own "tags". Relations can be used as members in other relations (nested or hierarchical structures). Each object participating in a relation can be assigned a role, for instance stop for a bus stop in the bus route, or platform for platforms related to according stop positions.

There ​many types of relations, but most popular are

type=multipolygon

A water object (natural=water), a building (building=*) or administrative boundary (admin_level tag).

(stub)

type=route

Used to describe bus routes and train routes along other transportation services. (stub)

type=restriction

Can used to describe turn restriction according to signs and road marking. JOSM has a plug-in to support this type of relations: ​http://wiki.openstreetmap.org/wiki/JOSM/Plugins/Turnrestrictions

​http://wiki.openstreetmap.org/wiki/Relation:restriction#Examples

Tags

A tag is a name/value pair assigned to an object. Tags are used to describe an object in detail. If we write foo=bar we mean The tag with key foo is assigned the value bar. Here are some examples:

  • name=Main road assigned to a way. This tag indicates that the name of the way is Main road.
  • amenity=restaurant assigned to a node. This tag indicates that the node represents a restaurant in the real-world.
  • route=bus assigned to a relation. This tag indicates that the relation represents a bus route.

Tags can be combined. An object can carry as many tags as necessary. Here's a more complex example: 

highway=residential
name=Main road
name:en=Main road
name:de=Hauptstraße
maxspeed=30
hgv=no
oneway=yes

Assigned to a way, this set of tags indicate, that the way represents a road in a residential area with name Main road (the German name be Hauptstraße, the English name, which in this example equals to name, is Main road). Speed is limited to 30km/h and heavy goods vehicles (hgv) are not allowed. Furthermore, it's a one way street.

You are free to assign an object whatever tag you feel necessary. However, there is a list of so called ​Map Features, i.e. a canonical list of tags with a well-defined meaning which are often used by mappers. Whenever possible you are advised to stick to these tags because map renderers, routing engines, and other pieces of software rely on them.

In the source:trunk/images/dialogs/propertiesdialog.svg Tags/Membership Dialog you can assign tags to an object, remove tags from an object, or edit assigned tags.

Object ids

The OSM server assigns each object a unique number, the object ID or OSM ID. A new object doesn't have an ID (it's ID is 0) until it is uploaded the first time to the OSM server.

  • Under Preferences -> source:trunk/images/preferences/display.png Display Settings -> Look and Feel it is possible to en- or disable the display of objects ids in the toggle dialogs.
  • With File -> source:trunk/images/downloadprimitive.png Download object ... it is possible to download objects by Ids.
  • View -> source:trunk/images/info.png Advanced info opens separated windows with informations about selected objects in text format.
  • View -> source:trunk/images/info.png Advanced info (web) opens the objects' pages of selected objects on the ​OSM website in your web browser.

Alternatively, you can browse the objects directly by entering following address in your web browser: 

https://www.openstreetmap.org/browse/[node/way/relation]/[ID]

Object versions

Each object has a version. The version is incremented whenever the object is uploaded to the server and the OSM server not only stores the most recent version of an object, but it's complete history.

  • View -> source:trunk/images/dialogs/history.png History opens the History Browser. The History Browser will show you the versions of a particular object.
  • Alternatively, View -> source:trunk/images/dialogs/history.png History (web) opens a page on the ​OSM website in your web browser which displays the object history, too.

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