[Talk-ca] Data imported from Geobase_Import_2009 and tags

Richard Weait richard at weait.com
Mon Mar 29 16:26:28 BST 2010

On Mon, Mar 29, 2010 at 9:59 AM, john whelan <jwhelan0112 at gmail.com> wrote:
> Could some one have a look at any of the roads that have been imported in
> this way especially in Orleans.  They appear to have a tag of "Ontario
> Canada" but no city tag.  Should "Ontario Canada" be two tags?
> Looking at the roads it Ottawa the city center seems to be Potlatch created
> again there is no city tag.
> How does the search engine know where the roads are when you do a search?

As I understand it, is_in= and addr:city=, addr:state=, tags on nodes
/ ways / and relations are deprecated in favour of a boundaries.

First, we create a boundary relation[1] for Orleans, and other
intersecting, overlapping relations for Ottawa, Ontario, Canada,
Ottawa City Parks, Local Water Protection District, etc.

That gives us nested / overlapping boundaries for these interesting
bounded places.  Smart tools like a postGIS select statement can tell
you how many houses are in Orleans, or what is the minimum distance
from Local Water Protection District to the city road-salt storage
barns.  Or can tell you that selected node #12345678 is contained in
boundaries Orleans, Ottawa, National Capitol Region, Ontario, Canada,
North America, Northern Hemisphere, Western Hemisphere, Earth, ...

It can also tell us the area contained by boundary or the common area
shared by overlapping boundaries.  And when a boundary changes or
moves (like voting area boundaries) only the boundary needs to be
updated on the map.

With is_in-type tags on nodes/ways/relations, to move the voting area,
we'd have to find those affected nodes, and change them.  And we'd
eventually have countless nodes tagged with endless levels of
boundary.  Too big and less flexible.

On the other hand, is_in-type tags were easier to use with simpler
tools like 'grep'.

So, what you see in Ottawa, without addr:city, is likely manually
added by a local Ottawa mapper and pre-dates the 2009 import.  The
geobase 2009 import was around the same time that is_in-type tags were
losing favour and the rise of boundary relations.  And it's certainly
possible to find stuff that has been combined or customized in other
wonderful ways.

[1] http://wiki.openstreetmap.org/wiki/Boundary

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