[OSM-newbies] Administrative boundaries

[James Ewen]

On Sun, Nov 9, 2008 at 4:43 AM, Thomas Wood <grand.edgemaster at gmail.com> wrote:

> This wouldn't work (although very nice conceptually), as noted, the
> renderers only look for boundary=administrative ways tagged as such at
> the moment.

So if you tag a relation as an administrative boundary, that's not
going to render?

> The original plan for boundaries is that you draw a way representing
> the whole boundary of a region. However, this was unfeasible for
> mapping sections of a boundary from ground sources, as opposed to mass
> imports. It also had the consequence of very large ways being produced
> that data clients were unable to handle.

Not to mention that it puts a whole bunch of ways on top of each
other... I used a road as the delineation between the areas adjacent
to Strathcona County. So that means that, at the very least, there are
3 ways stacked on top of each other between the nodes that make up
that border/road. There's a way defining the road, a way defining the
border of Strathcona County, and a way defining the border of the City
of Edmonton.

> The alternative method was proposed of marking a boundary way between
> two regions. When the region on one side of the boundary changes, you
> should start a new way (since at this point there'd be an intersection
> of at least 3 boundaries). You'd define what was on either side of the
> boundary by using region_name:left and region_name:right tags

Yeah, I've tried doing that for marking the provincial border...
Actually I've found that the provincial border did get rendered. The
biggest problem is the way it gets rendered. You have to be zoomed in
so close, that you can't tell what the line is supposed to represent.
If you zoom out far enough to be able to see the outline of the
province, the boundary doesn't get rendered. That seems to be a common
theme though... I live in a sparsely populated and developed area. I
am usually wanting to look at a large area around me, and am looking
for details that have been dropped many zoom levels previously. I'd
like to see that next town 20 miles away, and the roads to get there,
but I'm looking at a blank slate. In Europe, you'd probably have 3
cities in view at that level, and end up with a blob of colour that
you couldn't make heads nor tails of...

> Relations were then added to the mix - the boundary relation was
> proposed to tie up the boundary ways of an area together and use that
> to name the area they represent.

Could that relation boundary then be used to put a label on the area,
or a background fill colour?

> And finally, a more exact link of where you're editing will be of help
> - both Strathcona County and the bits of the Alberta border you've
> tried defining are quite difficult to find if you've got little
> knowledge of Canada!

Oh come on, cartographic experts like ourselves should know every nook
and cranny of the world... 8)

http://www.openstreetmap.org/?lat=53.3861&lon=-113.3246&zoom=13&layers=B000FTF

This area has a boundary between Strathcona County, the County of
Leduc, and the City of Edmonton. The City of Edmonton boundary was
defined by tracing the whole outline of Edmonton and creating an area.
Strathcona County was done the same way, but then I just recently
tried adding in the relation concept as well. The biggest difficulty
is having multiple ways stacked one on top of the other. I have to
delete ways to try and get to the way I am interested in. I'm not sure
exactly where I am at now in the process...

While we are on defining areas and such... Elk Island National Park is
an area that I have defined, which shows up to zoom level 10. After
that, it disappears.

http://www.openstreetmap.org/?lat=53.58&lon=-112.83&zoom=10&layers=B000FTF

Really it should be visible up to at least zoom level 8. There are
other much larger National Parks that I'm not going to bother defining
if they won't show up on the map unless you're zoomed in close enough
to not be able to see them. Here's a map image of Alberta.
http://yellowmaps.com/travel/travel_alberta/map.jpg

Even at this level, you can easily see Wood Buffalo, Jasper, Banff,
Waterton, Cypress Hills, and Elk Island National Parks, as well as the
Willmore Wilderness Area, along with the Provincial border. It's
things like this on the map that we use as landmarks for figuring out
what area we are looking at. OSM drops most of that information well
before you can get zoomed out enough to see them.

http://www.openstreetmap.org/?lat=53.54&lon=-111.84&zoom=8&layers=B000FTF

At zoom level 8, the city of Lloydminster is visible, which straddles
the Alberta Saskatchewan border. If I zoom in on Lloyminster, by zoom
level 7, the border is visible, but unless you know what you're
looking at, it's just a little purple line. You can't zoom out to
figure out what that line represents. How do we figure out at what
zoom levels the different administrative levels show up at?

I'm thinking perhaps in an area like Canada where you need to be
zoomed out to zoom level 5 before you can see the province, perhaps we
should look at moving the national boundary up to admin_level 1, and
the provincial boundary up to admin_level 2. Hmm, can you define a
boundary with multiple admin_levels so that it shows up across a wider
range of zoom levels?

Here's the SE corner of the province of Alberta...
http://www.openstreetmap.org/?lat=49.004&lon=-109.991&zoom=14&layers=B000FTF

Potlatch has a little hiccup with these borders... if you go into
Potlatch, the way ends up being displayed about 50 pixels wide. It
makes it a little difficult for editing. That, and the American border
import from Tiger data needs some clean up. The US counties seem to
like to encroach on our sovereign nation! Is there a way to get
lat/long information for a node in Potlatch? It would help in putting
the corners of the province in the right place.

So many questions...

James