[OSM-talk] [OSM-dev] Polygons and Multipolygons

[Robert (Jamie) Munro]

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Artem Pavlenko wrote:
| On 8 Feb 2008, at 11:50, Frederik Ramm wrote:
|
|> Hi,
|>
|>> I found the way term 'Multipolygon' is used in OSM context is
|>> confusing.
|> True. What we had been looking for was a term for "polygons with
|> holes"; it seemed unreasonable to create a relation "type=polygon"
|> as plain polygons, without holes, don't require relations. But
|> multipolygon is somewhat of a misnomer.
|>
|>> Shouldn't we be calling MultiPolygon  Polygon?
|> There are only 2788 in the database so it would not be too hard to
|> change. I wanted to automatically add the "inner" and "outer" flags
|> to the existing polygons anyway, although they're not strictly
|> required they would make processing easier for some.
|
| I think having 'outer' and 'inner' flags/tags will help at the data
| entry stage as well.

Can't we use clockwise / anticlockwise rules? The colour is on the
right, therefore polygons run clockwise, holes run anti-clockwise,
islands inside those holes run clockwise again. Under this model, the
sea is a (normally blue coloured) polygon, and the land is a hole in the
sea. AFAICT, this is how it is drawn by the renderers at the moment (the
land colour is just the default rendering background colour).

Robert (Jamie) Munro
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