Context Navigation

Editing Help/Concepts/Object

Adjust edit area height: Edit side-by-side

[[TranslatedPages]]

= 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 overhelming complexity of real-world objects you can map, JOSM provides only three kinds of objects as basic building blocks for maps: '''nodes''', '''ways''', and '''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.

[[TOC(inline)]]

== Nodes, ways, and relations ==

* [[Image(source:/trunk/images/data/node.png)]] - a  '''node'''  is an individual point with a defined position.

* [[Image(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 respresent a river, the boundaries of a country, or even a building. If a '''way''' is closed, i.e. if the last node is the same as  the first node, it is also called an '''area'''.

* [[Image(source:/trunk/images/data/relation.png)]] - a '''relation''' is an sequence of other objects, for instance a sequence of '''ways''' (representing road segments) and '''nodes''' (representing bus stops) which represent a bus route. Each object participating in a '''relation''' can be assigend a '''role''', for instance `stop` for a bus stop in the bus route, or `forward` for a road segmente which is part of the bus route from the start to the terminal station.

== Tags == 
A '''tag''' is a name/value pair assigend 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 two 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=living_street
name=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 living street with name ''Main road'' (the german name be ''Hauptstrasse''). 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 [http://wiki.openstreetmap.org/wiki/Map_Features Map Features], i.e. a canonical list of '''tags''' with a well-defined meaning which are often used by mappers. Whenever possible you are adviced to stick to these tags because map renderers, routing engines, and other pieces of software rely on them.

In the [[Image(source:/trunk/images/dialogs/propertiesdialog.png)]] [wiki:Help/Dialog/Properties Properties/Memberships 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.

* TODO: how to enable displaying of object ids 
 * TODO: download object you now the id of
 * TODO: browse an object with a specific id on the server

== 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'''.

In the [[Image(source:/trunk/images/dialogs/history.png)]] [wiki:/Help/Dialog/History History Dialog] you can load the '''history''' of an object and launch the [wiki:/Help/Dialogs/HistoryBrowser History Browser]. The History Browser will show you the '''versions''' of a particular object.

Alternatively, [[Image(source:/trunk/images/about.png)]]''Tools->Object history'' redirect you to a page on the [http://www.openstreetmap.org OSM website] which displays the object history too.

----
Back to [wiki:Help Main Help]

Note: See WikiFormatting and TracWiki for help on editing wiki content.

Change information

Your email or username:

E-mail address and name can be saved in the Preferences

Comment about this change (optional):

Note: See TracWiki for help on using the wiki.