[OSM-newbies] Administrative boundaries

[Thomas Wood]

2008/11/9 James Ewen <jewen at shaw.ca>:
> 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?

It will render based on how the ways are tagged. However, relations
should still be added and tagged for data-completeness, and future
possible uses of them.
>
>> 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.

My interpretation of the border tagging method is 1 way representing
the shared Strathcona and Edmonton border, as opposed to one
representing each county.
Stacked ways is an issue with the editors, none of them support it
particularly well, but potlatch probably is trickiest.
Select a node that has two ways sharing it and hit / to cycle between
the ways that use it.

>> 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...

Yeah, renderers need to be more clever at considering the feature
density of an area.

>> 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?

Hopefully in the future!
>
>> 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...

I'm going to use JOSM to look over the data you've got entered, it's a
much better editor for the large-scale edits of borders. Plus it's
slightly easier to see overlapping ways (middle clicking)

Ok, the first thing I note is that all the ways are tagged
boundary=civil, rather than boundary=administrative.
A minor point is that the names aren't strictly supposed to be defined
by left and right tags but conty:left and county:right (or something
similar, I can't remember the exact scheme, but left and right will do
for now :)

I note that several sections of the Edmonton border are duplicated, in
particular, it seems that 3 identically tagged borders run over the
north west corner of the city.

I'll have a tidy up...

> 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 where I should say "don't tag for the renderers", although it's
nice to see the data, they cannot possibly show all features at all
zoom levels. I know there is particular issues with these lowzoom
situations. There's currently no easy way for them to filter by the
size of a feature to bring it up to the lower zooms without
compromising the look of more densely packed areas.

> 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

Yes, there so often is with OSM :)

-- 
Regards,
Thomas Wood
(Edgemaster)