[Talk-ca] Large polygons in JOSM

Daniel Begin jfd553 at hotmail.com
Mon Sep 15 21:41:20 UTC 2014



Well, I understand that multipolygons are often not easy to work with. However, from what I understand of OSM data model, they should be used whenever appropriate.


In that sense, I do not agree with Bruno that 'inner' roles are useless for lakes in the case of wooded areas. It might be OK for rendering (you see lakes inside wooded areas because priorities have been used to create the map) but, IMHO, it is not the case if you work only on wooded areas – or any feature type!


About Canvec, the product often duplicates water bodies and inner polygons of wooded areas; which is not necessary where both were imported. In order to keep only the necessary geometries, I usually transfer all the tags from a waterbody to the duplicated geometry of an inner polygon and then, I delete the original - now duplicated - waterbody.


a humble two cents...



From: Bruno Remy [mailto:bremy.qc.ca at gmail.com] 
Sent: September-15-14 12:59
To: Tom Taylor
Cc: Sam Dyck; Talk-CA OpenStreetMap
Subject: Re: [Talk-ca] Large polygons in JOSM


Tom's strategy seems to be appropriate for woods areas:

Canvec 'giant monster' multipolygons represents a set of several polygons quite closed but not adjascent ,  mostly separated by  meadow/scrub or fire cut-lines or rivers, or roads ....

By the way: membership as 'inside' role of wood multipolygon is useless for a lake

So, you never need 'outside' or 'inside' role: just keep outlines of wood.

Mapping this way avoid the use of multipoygons, and encourage the use of simple polygons (prefered).


Simplier is better ;)

But .... indeed.. i agree with Sam: is time consuming ! :(

Perhaps a motivation to encourage membership of new OSM contributors, as we celebrate the 10th of OpenStreetMap !! ;-)

The more we are.. the less we do ;)





2014-09-15 11:46 GMT-04:00 Tom Taylor <tom.taylor.stds at gmail.com>:

Might be dull, but I generally split multipolygons into reasonably-sized adjacent chunks rather than giant monsters. In my case, it's usually when I'm outlining a river.

Tom Taylor

On 14/09/2014 10:29 PM, Sam Dyck wrote:


Currently I'm working on importing the Canvec tiles that make up Lac
Seul in NW Ontario into OSM. Importing the data as it is, split into
tiles and subtiles, is poor practice, and manually merging is time
consuming and dull. So I began using JOSM's Join Overlapping Areas
feature. This tool however requires that all ways be complete before
merging. Resulting is a 100 000 node area that far exceeds JOSMs import
limit and is time consuming to split up, and slows down JOSM. Is there
an faster way to split this?


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Bruno Remy 

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