Relation:multipolygon

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multipolygon

Image:None-yet.jpg

Description: This relation is used to represent areas with holes. Google definition User discussion

Group: Properties

Members: help - outer - inner

Tagwatch: help Europe France Germany Italy Netherlands Spain Turkey United-Kingdom

Relations of type multipolygon are used to represent areas with holes. Such relations have been automatically created wherever there was an "area with a hole" in the 0.4 data, modelled as one way with two rings of segments.

In short, an area with holes consists of an outer polygon tagged like a usual area, and several inner polygons as the marker for the inner edge of the area. Do not copy tags from outer polygon to inner polygons.

Tags

Key	Value	Discussion
type	multipolygon

Members

Way or Node	Role	Recurrence?	Discussion
	outer	one	The outer ring of the area
	inner	one or more	An inner ring of an area (Example: an island in water)

Notes

The intended use of multipolygons is this:

• Tags describing the multipolygon should go on the outer way.
• The inner way(s) may be left untagged.
• If the inner way represents something in itself (e.g. a forest with a hole where the hole is a lake), then the inner way may be tagged as such.
• The direction of the ways does not matter.

This was confirmed on a relations workshop we did during State of the Map, 2008.

(as of 2008-09-10 in mapnik renderings it does matter in which direction the ways go - it works if the outer one goes clockwise and the inner ones go counterclockwise)

step by step guide

JOSM

A summary of the steps to create this relation using JOSM based on a list from Jon Burgess.

1. Create the outer ring (direction does not matter), and tag it according to the area (e.g. natural=water).
2. Create the inner ring (direction does not matter). Do not tag it.
3. Make sure you have the 'Relations' information open by enabling the relation icon (the bottom on the list down the left hand side).
4. Select all the ways needed for your relation.
5. In the relation box click 'New'.
6. A new window appears. Click 'Add Selected' to add the selected ways into the relation.
7. In the top half of the 'Relations' window, click on the blank box below key and enter 'type'. Under value add 'multipolygon'.
8. Then you need to define the 'role' for each way. Click on each of the ways, and use the 'Select' button in the dialog to highlight this in the main map window.
9. Set the 'role' value for each inner ring to 'inner', and for the outside ring set the role to 'outer'.

• There is a German screencast showing these steps (TODO: Verify whether screencast still has obsolete references to direction and tagging the inner ring like the outer.)

Merkaartor

1. Open the area you want to edit. (File -> Download from web -> ...)
2. Select all ways you need in the relation (hold Ctrl and mark/select the ways with mouse)
3. Select from the program menu Create -> Relation
4. Now there is a table with the fields Role (unfilled) and Member (filled with data of selected ways)
5. Type the word "outer" for the outer way and "inner" for all inner ways.

If you don't know which way is inner or outer, select the outer way and remember the last few digits of the way ID of this way. Start again. Now type in "outer" for the way with that number. All other ways should be logical "inner" ways.

Potlatch

1. Create the outer way (direction does not matter). Tag it as appropriate (e.g. natural=water).
2. Create the inner (hole) way(s) (direction does not matter). Do not tag them.
3. Select the outer way and click on the second symbol on the right side, which looks like two chain segments.
4. "Create a new relation" should be selected; click "Add".
5. Type in the word "type" in the first field (key) and "multipolygon" in the second field (value) and click "ok".
6. Now there is a additional field which looks different from the other key/value input fields. This field describes the "role" of the way. Type in the word "outer" for your outer way.
7. Select one of the inner ways and click on the "chain link"-symbol. Do not select "Create a new relation", but instead, select your created relation in the dropdown menu. This should be the one with the highest number in the list. Click "Add" to add the way to the selected relation.
8. In the field near the word "multipolygon" type in the word "inner" to mark an inner way.
9. Repeat 8 for every other inner way.