Large areas such as national parks

gdal · 2012-06-23T01:03:34.000Z

Hi Everyone, newbie to OSM, please be nice

I have the boundaries of a large national park in Australia, Victoria which is currently missing in OSM database.

using JOSM, the area contains over 80,000 nodes which is to many nodes (max is 2k?).

Here are my questions:

I’m thinking of Splitting this way into many ways using the splitways tool, is this the right approach?
Once split, do i need to tag the start and end nodes with a relation so the database knows these ways are part of one large area?
I’ve tagged it’s property with key=boundary:national_park, Value=Alpine National Park. Is this all that’s needed?

MikeN1 · 2012-06-23T11:08:29.000Z

You are correct about splitting into many ways using the splitways tool. Check all that the ways are not ‘over-noded’, using the JOSM Simplify Way tool.

For tagging, the ways would contain no tags, but would all be members of a multipolygon relation.

type=multipolygon
boundary=national_park
leisure=park
name=Alpine National Park
wikipedia=Alpine National Park
website=

Each way would have a role of “outer” in the relation.

Tordanik · 2012-06-23T11:33:14.000Z

Boundaries of large areas are usually mapped as multipolygon relations.

For the national park, you would:

split the area into shorter ways

create a relation

add at least the 3 following tags: type=multipolygon ; boundary=national_park ; name=Alpine National Park

add the outline ways as members with the role “outer” to your new relation

remove the name and boundary tags from the outer ways

Edit:
It seems that MikeN was faster to reply, but our postings mostly agree anyway. There are only a few small things I’d do differently. The advice to check whether the ways have more nodes than necessary is useful, but don’t blindly use the Simplify Way tool - it’s often overzealous and deletes relevant information. As for leisure=park, that tag is normally used on smaller parks in cities rather than national parks, a distinction that is explicitly mentioned on Tag:boundary=national_park. Also, using wikipedia=**en:**Alpine National Park as the Wikipedia link would avoid ambiguities by explicitly linking to the English edition of Wikipedia.

gdal · 2012-06-25T04:05:52.000Z

Is a polygon with no holes a multipolygon too? I guess not right?

JRA · 2012-06-25T06:03:19.000Z

Any polygon can be expressed as multipolygon according to OGC Simple Features specification (which OSM does not totally follow). Polygon is limited to have one outer ring and zero or more inner rings while real multipolygons have several outer rings. Most OSM multipolygons have only one outer ring and some holes so they could be called just polygons but at the same time they are also simple multipolygons. Wiki page http://wiki.openstreetmap.org/wiki/Relation:multipolygon does not have an example of a multipolygon relation with only one outer ring and no holes but I think such a thing would suit your national park well.