[Talk-us] Multipolygonizing

[Rihards]

On 2017.11.20. 00:48, Douglas Hembry wrote:
> Greetings everyone,
> I've just had a short changeset discussion with mapper glebius prompted 
> by changeset 46612750 "Properly multipolygonize Monterey coast line". My 
> understanding is that the map of this stretch of coastline has been 
> restructured to avoid adjacent ways that share nodes. Accordingly, only 
> a single way ever connects any set of nodes, and the single way 
> participates, if necessary, in multiple relations. A result of this is 
> that in a high density area like downtown Monterey Bay many small areas 
> like building footprints or pedestrian areas are defined as distinct 
> multipolygons, with several ways (outers) making up the outline. An 
> example at:
> 
> https://www.openstreetmap.org/#map=18/36.61726/-121.90045
> 
> (look at Hovden Way near the top, or the outline of 700 Cannery Row, 
> further down near Bubba Gump, comprised of seven outer ways)
> 
> glebius believes that this approach (with the help of the reltoolbox 
> JOSM plugin) is easier and less error-prone than having multiple simple 
> closed ways (eg, a building footprint and an adjacent pedestrian area) 
> sharing a set of nodes on their adjacent boundary. . (I hope I'm 
> representing this accurately, glebius will correct me if I'm getting it 
> wrong).
> 
> In my limited experience I've never encountered this before, and at 
> first sight I'm not convinced, particularly when considering future 
> maintenance. I told glebius that I wanted to find out  what the 
> community thought. Is this just one more valid optional way of mapping? 
> To be recommended for adoption if possible? Or to be avoided? Thoughts?

not an authoritative opinion : it's terrible. mapping contiguous areas
as multipolygons results in data that is extremely hard to modify (think
splitting landuse from a building) and is more than a minefield for newbies.

personally, i either redo these as separate ways when i have the time
(original authors do not object as they have went either mad or out of
energy after working with multipolygons too much), or give up and leave
the area outdated - i don't have the skills to maintain that.
-- 
 Rihards