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#1 2017-08-30 19:01:17

userJeff
Member
Registered: 2017-07-13
Posts: 4

Parks bounded by roads

In many cases, especially in urban areas, parks are bounded by roads. One method of adding a park to the map is to use the existing ways  that define the roads as the park boundary. (This can be done by either connecting nodes of a separately created park area or by using the road segments as members of a multipolygon.) The other method to add a park is to create a separate park area that more or less parallels road boundaries. So far I have preferred to use the former for the following reasons:

1)Better Representational Efficiency- Why use two almost identical sets of nodes to define something when it can be done with one?
2)Cleaner Looking Map- Rendered map does not contain a potentially jagged gap caused by the park boundary and road not being perfectly aligned.
3)Quicker to Add- Creating a separate way and being careful to make it parallel to the existing one is more time consuming.

A few concerns I have gathered from others regarding this method are:

1)More difficult to edit if park boundary or road changes.
2)Park boundary may not technically lie on centerline of road.

Concern 1) seems valid as there are cases where the road and park boundary move independent of one another. But there are other cases where the road moves and carries the park boundary with it. In that case, having a single way representing both the park and road would be advantageous. The weight of this concern depends on the relative frequencies of the different types of changes.

Concern 2) is valid if the park boundary is known exactly, say 18 feet offset from the centerline of the road. But in cases where this level of detail is not known, the centerline of the road is a simple, happy medium approximation. The actually boundary could be 18 feet to the inside or the outside. Why guess one or the other and potentially be up to 18*2=36 feet off the actual boundary? I'm referring to cases where the road is the practical boundary between the parkland and the surrounding area. For example, one side of the road is grass and trees and the other side are resident's lawns and driveways.

Any thoughts?

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#2 2017-08-31 04:16:55

escada
Moderator
Registered: 2011-08-13
Posts: 1,750

Re: Parks bounded by roads

Short answer: never attach road to landuse (leisure=park is kind of a landuse).

The line for the road represents the middle of the road, the park does not extend to the middle of the road. One has to leave room for an area:highway which represents the extend of the road. It's better not to connect it to the road, even if you do not know whether the gap between the park boundary is 5, 10 or 20 meters. The mistake in the size of the gap is less of a problem than connecting the park to the middle of the road.

Suppose you want to map the fence around the park, do you really want to let it coincide with road ?

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#3 2017-08-31 09:35:57

hadw
Member
Registered: 2014-09-02
Posts: 1,081

Re: Parks bounded by roads

+1

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#4 2017-08-31 12:11:16

nevw
Member
From: SE Queensland, Australia
Registered: 2013-04-11
Posts: 425

Re: Parks bounded by roads

+1

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#5 2017-09-02 05:28:55

Viajero Perdido
Member
Registered: 2016-10-13
Posts: 172

Re: Parks bounded by roads

-1

If someone wants to add extra levels of detail - such as a fence - THEY can pull the park boundary away from the road and put in the extra effort in making it all line up just right.

There IS such a thing as too much detail.

Matter of opinion of course, and that's mine.

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#6 2017-09-02 06:44:55

nevw
Member
From: SE Queensland, Australia
Registered: 2013-04-11
Posts: 425

Re: Parks bounded by roads

I would rather the extra effort in to do it correctly at the start instead of other mappers having to undo the previous edit to add more detail.
Matter of opinion of course, and that's mine.

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#7 2017-09-02 07:02:50

escada
Moderator
Registered: 2011-08-13
Posts: 1,750

Re: Parks bounded by roads

@Viajero Peridido: having the road and the landuse collapse is not a matter of detail, it is just wrong for me.
What you do gain with letting them fall together  ? A little less points in the DB ?

Your solution, and having two different landuses that overlap a road are among my top annoyances, as they are so time consuming to fix.

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#8 2017-09-02 11:52:12

henke54
Member
Registered: 2015-03-17
Posts: 733

Re: Parks bounded by roads

escada wrote:

Short answer: never attach road to landuse (leisure=park is kind of a landuse).

Also, even when landuses are attached to each other,and someone wants to map a new road or waterway in that area, it is afterwards, a whole hassle to 'detach' those landuses and place them on the correct position ->
snap2.png

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#9 2017-09-02 15:03:58

userJeff
Member
Registered: 2017-07-13
Posts: 4

Re: Parks bounded by roads

Another option to reuse the same road way for the boundary is to create a multipolygon with the surrounding roads as the members. (Seperate member ways can be created for where the boundary may diverge from the road).But I'm not sure if this is typically easier to edit versus attaching the two ways together.

I'm not sure its so rare that the centerline of a road or river conicides with a boundary. It seems at least in the United States that roads are often layed on top of administrative boundaries and I dont see why parks would be an exception. As far as a fence being placed around the park in that case, that would require a seperate way as the fence would be inside the park boundary.

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#10 2017-09-02 16:03:19

Viajero Perdido
Member
Registered: 2016-10-13
Posts: 172

Re: Parks bounded by roads

As far as most users of the map care, the road IS the boundary.  Mapping it this way provides a clean look in every renderer* I've looked at, and it's much simpler to map.  For example:  http://www.openstreetmap.org/#map=15/54.3999/-116.8009

A related issue:  If something like landuse=residential covers a wide area, do you really expect each city block to be mapped separately to provide those technically accurate gaps?  In my mind it's perfectly acceptable for a road to go through a landuse.  Or have I missed a firm rule somewhere?

* PS, I don't call that simplification mapping for the renderer.  I'd call it mapping to a chosen level of accuracy.  Maps are all about selective accuracy.  It's why we don't (most of us don't) map individual trees, many of us can't be bothered to map individual houses, etc.

Last edited by Viajero Perdido (2017-09-02 16:12:30)

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#11 2017-09-02 17:15:01

henke54
Member
Registered: 2015-03-17
Posts: 733

Re: Parks bounded by roads

Viajero Perdido wrote:

As far as most users of the map care, the road IS the boundary.  Mapping it this way provides a clean look in every renderer* I've looked at, and it's much simpler to map.  For example:  http://www.openstreetmap.org/#map=15/54.3999/-116.8009

About 'accuracy', as far as i can see on your link, is that the road is NOT the boundary of the forest, ->
Fox_Creek.png
and (in my country anyways) are the 'actual boundaries' usually waterways (often beside the road) . wink

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#12 2017-09-02 21:17:45

Viajero Perdido
Member
Registered: 2016-10-13
Posts: 172

Re: Parks bounded by roads

Right.

Not perfect until someone wants to take the time to make it so.

My guiding principles are, better than before, and good enough for now.

I added that forest and landuse, then moved on.  There are so many other things, mappy or otherwise, demanding of a volunteer's attention.  smile

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#13 2017-09-03 07:09:34

escada
Moderator
Registered: 2011-08-13
Posts: 1,750

Re: Parks bounded by roads

Viajero Perdido wrote:

A related issue:  If something like landuse=residential covers a wide area, do you really expect each city block to be mapped separately to provide those technically accurate gaps?  In my mind it's perfectly acceptable for a road to go through a landuse.  Or have I missed a firm rule somewhere?

Through is no problem for me, but I think it is incorrect to have a field and forest be connected on e.g the left side of a road, when the road is actually between the two.

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#14 2017-09-03 07:12:32

escada
Moderator
Registered: 2011-08-13
Posts: 1,750

Re: Parks bounded by roads

Viajero Perdido wrote:

As far as most users of the map care, the road IS the boundary.  Mapping it this way provides a clean look in every renderer* I've looked at, and it's much simpler to map.  For example:  http://www.openstreetmap.org/#map=15/54.3999/-116.8009

<sarcasm> thanks a lot for creating more work for the mappers after you.</sacarsm>

this is mapping for the renderer. sorry, but this is a bad practice.
Don't understand why it is simpler. Draw a line next to the existing one is as easy as drawing it on top of the other.

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#15 2017-09-03 17:00:17

Viajero Perdido
Member
Registered: 2016-10-13
Posts: 172

Re: Parks bounded by roads

We're splitting hairs now.  Mapping something incorrectly on purpose (eg for the renderer) is bad; I won't dispute that.  Mapping something with coarse accuracy is another story.  Coarse accuracy is fine at a certain conceptual zoom level (IMHO), and someone with more time on their hands can add accuracy later.

I don't think I created more work in the linked example because someone may look at it and say, good enough, and not feel the need to take it any further.  In this part of the world, we have plenty of unmapped areas more deserving of attention.

Happy mapping,
VP

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#16 2017-09-03 17:07:32

hadw
Member
Registered: 2014-09-02
Posts: 1,081

Re: Parks bounded by roads

Once someone has mapped a boundary wrongly, it is much less likely that anyone will correct it than that they would map it correctly if it wasn't there at all.

People prefer new mapping to maintenance.

People are not comfortable with correcting other people's work, unless it stands out like a sore thumb as being wrong.

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#17 2017-09-03 19:20:38

escada
Moderator
Registered: 2011-08-13
Posts: 1,750

Re: Parks bounded by roads

VP, each time you have to split the road to add different properties to some sections, you well regret that you attached the road to the landuse. Believe me, I have read about this topic several times, when people started adding more and more detail and complained that the previous mappers attached landuse and roads.

Or what if people start mapping separate sidewalks, will they run through the forest in your map, while they do not do that in reality?
What if people want to start adding area:highway to really map the extend of the road ?

These are topics that people will start doing as soon as the basics are mapped. They will not like your style of mapping, sorry to say so.

As for the mapping for the renderer, you are attaching the landuse to a line that represents the middle of the road. That's mapping for the renderer for me.

Happy mapping, to you too.

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#18 2017-09-03 20:20:55

Viajero Perdido
Member
Registered: 2016-10-13
Posts: 172

Re: Parks bounded by roads

Fair enough.  Those are valid concerns, and mappers should be aware of them.

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