OpenStreetMap Forum

Steven @ Microsoft

Member

Registered: 2017-12-12

Posts: 47

Waterways: Can someone clarify what "inner" and "outer" means?

I have noticed that there is a relationship between the boundary of a waterway and the land. If you take for example the Island of Lake Bled.

For example: got to https://www.openstreetmap.org/way/25436 … 39/14.0953

You will see Lake Bled. Zoom in to https://www.openstreetmap.org/edit?rela … 1/14.08671 and tap on the line around the lake and you will the properties of the lake boundary appear. On the left I see "All Relations" of which there is one called "Lake Bled" with a value of OUTER.

If you now go to the island in the middle of the lake at https://www.openstreetmap.org/way/81495 … 1/14.09005 and tap on the line that circles the island (e.g. at https://www.openstreetmap.org/edit?rela … /14.08996) I see that this line also has one relation called "Lake Bled" but with a value of INNER.

Can someone clarify what the OUTER and INNER mean here? I am guessing that OUTER is the "outer boundary" of an entity but INNER is a boundary "within" in the entity. Is this correct?

muralito

Member

Registered: 2012-09-04

Posts: 1,918

Re: Waterways: Can someone clarify what "inner" and "outer" means?

See https://wiki.openstreetmap.org/wiki/Rel … ltipolygon

althio

Member

Registered: 2014-12-09

Posts: 36

Re: Waterways: Can someone clarify what "inner" and "outer" means?

Can someone clarify what the OUTER and INNER mean here? I am guessing that OUTER is the "outer boundary" of an entity but INNER is a boundary "within" in the entity. Is this correct?

You are mostly right.
A relation:multipolygon is built using these 2 ways, 1 outer way and 1 inner way.
This is the "real" lake entity: https://www.openstreetmap.org/relation/646
See also some documentation: https://wiki.openstreetmap.org/wiki/Rel … inner_ring

hadw

Member

Registered: 2014-09-02

Posts: 1,081

Re: Waterways: Can someone clarify what "inner" and "outer" means?

Note the name on the inner way serves no useful purpose, as there is no longer a main tag, and the tags on the outer way are probably obsolete, as well.

Steven @ Microsoft

Member

Registered: 2017-12-12

Posts: 47

Re: Waterways: Can someone clarify what "inner" and "outer" means?

Thanks very much for the answers. Very useful stuff.