[OSM-talk] Best way to draw areas with holes?

[Jon Burgess]

On Thu, 2007-12-20 at 19:59 +0200, Rahkonen Jukka wrote:
> > Use the multipolygon relation.
> > It'll be rendered by the Mapnik layer at least.
> > http://wiki.openstreetmap.org/index.php/Relations/Multipolygon
> 
> > Unfortunately you can't do that in Potlatch yet, so you'll need to be
> > using JOSM or some other editor which supports relations.
> 
> Hi,
> 
> I tried to read and understand relations, and concluded that their main purpose probably is to keep newbies out of here :) 
> 
> Could some kind person explain to simple minded me what should I actually do if I have one outer ring and one or more inner rings and I want to make a polygon with correct number of holes out of them with relations? How on earth can I select the rings which belong together and tell which is outer and which are inner ones? Or is there already a how-to somewhere in wiki?
> 

1) Create the outer and inner rings each as a single way.
2) Make sure you have the 'Relations' information open by enabling the
relation icon (the bottom on on the list down the left hand side).
3) Select them all the ways for you relation
4) In the relation box click 'Add'
5) A new window appears. Click 'Add Set' to add the selected ways into
the relation
6) In top half of the window click on the blank box below key and enter
'type'. Under value add 'multipolygon'
7) Then you need to define the 'role' for each way. Click on each of the
way members in turn an then use the 'Select' button in the dialogue to
highlight this in the main map window.
8) Set the 'Role' value for each inner ring to 'inner', and for the
outside ring set the role to 'outer'.

Note that many existing multipolygon relations do not have the 'role'
set.

  Jon