[talk-au] National Park unclosed poly, want advice

Paul Norman penorman at mac.com
Tue Apr 21 19:41:03 UTC 2015


On 4/18/2015 11:35 PM, Nathanael Coyne wrote:
> I'd appreciate if someone could have a look at it and tell me if it is 
> valid or invalid and if invalid then where I should start with fixing 
> it up, given it covers such a large area.
>
> http://www.openstreetmap.org/way/204064026#map=10/-35.8657/150.1611
The way itself isn't a polygon, but is part of the multipolygon 
http://www.openstreetmap.org/relation/1388357

It is valid, but an area this large is a problem to deal with for a 
number of reasons
- You're more likely to conflict with people editing it
- Checking validity is hard, as you need the entire  polygon
- It poses problems for rendering toolchains

Coming from an area with many areas of trees, I have a few techniques. 
One is to end up splitting on an arbitrary line. While this fixes the 
problems, it's not ideal. A better route is to find an appropriate break 
in the trees.

Typically along roads, rivers, power lines, and oil and gas lines there 
is a break in the trees. I try to find one and trace this break. This 
also tends to find clearings 
(https://www.openstreetmap.org/#map=15/-35.8707/149.9854), unmapped 
roads branching off, and other features of interest.

Don't feel you need to be perfect, particularly in a case like this 
where the original tracing is from landsat.



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