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<p style="margin: 0 0 1em 0; color: black;">In the same manner, in some US
states, cities and towns are subordinate to counties. In some other US
states, such as Virginia, towns are subordinate to counties but cities are
on the same administrative level as counties.</p>
<p style="margin: 0 0 1em 0; color: black;">-- <br>
John F. Eldredge -- john@jfeldredge.com<br>
"Darkness cannot drive out darkness; only light can do that. Hate cannot drive out hate; only love can do that."
-- Martin Luther King, Jr.<br>
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<p
style="color: black; font-size: 10pt; font-family: Arial, sans-serif; margin: 10pt 0;">On
January 11, 2015 2:42:44 PM André Pirard <A.Pirard.Papou@gmail.com>
wrote:</p>
<blockquote type="cite" class="gmail_quote"
style="margin: 0 0 0 0.75ex; border-left: 1px solid #808080; padding-left: 0.75ex;">
Hi,<br>
<br>
Look at <a href="http://www.openstreetmap.org/relation/52411">the
Belgium relation</a> and, while hiding the subareas (in left
pane), try to figure with that map the <b>administrative tree</b>
(regions, provinces) using the borderlines. You won't.<br>
Now look at the subareas and something you will notice is that
Brussels is not inside any area. It has got its own independent
status. Not obvious at all from borderlines.<br>
Now, trying to figure the tree, you can use your knowledge of
Belgium or try to right-click on each subarea to open its link in
another browser tab and you will find that Belgium is divided in two
regions: Flanders in the North and Wallonia in the South.<br>
Now what about the other subareas? Try to jigsaw puzzle them again
and you will fit Flemish Community in the North, French Community in
the South and German community to the East. And so what about
Brussels again? It's Flemish-and-French bilingual.<br>
So, Belgium=Flanders+Brussels+Wallonia regions.<br>
and Belgium=(Flemish+bilingual+French+German) communities<br>
Similarly, United Kingdom=England+Wales+Scotland.<br>
I may miss a few UK details, but that's because ... it has no
subareas to see.<br>
And I recall a guy from Munich. Wasn't his problem that Munich is
not part of its Land?<br>
Isn't the Munich problem like Brussels (please do not focus the
thread on that if it's wrong).<br>
<br>
And the same process can be repeated at each boundary level down the
tree.<br>
<br>
Moreover, it is straightforward for a consumer program like OSM.org
to use the subareas to draw the outline of the regions, provinces,
etc. inside the country map or to do other things like measuring
borderlines. Why the heck would we remove the subareas and cause
those programs to stop working, instead of adding the subareas which
is really straightforward too?<br>
<br>
Now, there is a very interesting property of subareas making a nice
program.<br>
Choose a boundary relation. Pick its subareas members one by one and
put their borderline ways (members) in a bag. Now, remove those
ways that appear twice in the bag. What have you got? The
borderline of the chosen relation.<br>
For example, by combining that way the borderlines of the UK
subareas England, Wales and Scotland, you get the borderline of
United Kingdom. Idem down at any level.<br>
So, it looks like masochism somehow to tag borderlines for anything
else than the lowest level. From it, one may have that program
compute the borderlines of every relations upwards.<br>
But I guess software having to build a country boundary that way
would have a hard CPU time.<br>
The idea that would come to mind is to keep the borderlines as a
cache. But we have the cache already made manually. Why not simply
let the mappers use the program to build the borderlines manually?
They don't change often.<br>
<br>
That program can work two ways. Either to compute borderlines.
Either to check that the intricate borderlines match the so easily
tagged, error proof subareas.<br>
There is presently no real QA program for borderlines. Here it is.
Ad it's soooo easy...<br>
Start checking Belgium and France, Osmose! <br>
<br>
It's a really simple program, a very few tens of lines. I didn't
write exactly that but that was close (computing total length of
boundaries in a province or country). But, shame on me, I misplaced
the source :-(<br>
<br>
I once read on some server a French text wondering whether the right
solution is subareas <b>or</b> borderlines. As it often happens,
the answer is hard to find because the question is wrong. It is not
"or" but "<b>and/or</b>". And the answer is "and", both.<br>
Also wondering which makes tagging boundaries the easiest.
Certainly creating the boundary relations with just simple subareas
linking them. Then start adding borderlines at the lowest level.
And run the check program above working at progressively higher
levels. That programs detects incomplete borderlines loops and
hence dangling lines near which more have to be filled in. Visually
checking with the spoken above rendition that there are no unwanted
holes also checks the subareas tree.<br>
That's how we, Marc, André and Patrick (yes, MAP!) made the
boundaries of South Belgium.<br>
<br>
One thing is certain. Should anyone remove our subareas because, as
said, he does not understand, it would be like stealing a worker's
tool and I would stop any boundary work immediately.<br>
<br>
I won't write too much in one article but I'll add this. What's
that aversion against redundancy?<br>
Redundancy used as crosscheck is used in many place. For example,
TCP, which is the transport protocol of the Internet, uses
redundancy to make sure that these words I wrote came to you
intact. Same on a disk drive surface to make sure the recording is
correct. Etc.<br>
Should we remove the non-English pages of our wiki because they are
redundant?<br>
No, because they have different usage and it's the same with
subareas and borderlines.<br>
Except that for the latter we have a program to check consistency.<br>
<br>
Cheers
<br>
<br>
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<td>André.</td>
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