Roads through boundaries, corridor/void or not?

RobNicholson · 2018-08-31T00:25:32.000Z

Hi All,

I am currently working on tracks and roads going through a single National Park (multiple polygon object). The picture below shows a corridor/void around the road. I often run into this mapping style. I believe this is unnecessary and the road should go through the single National Park polygon. I would understand mapping it if the gap was significant, or their was someone different manages the corridor (different from the National Park or road). The additional polygons make it harder to edit, visually more complex than what it needs to be, I don’t believe it adds any value. Before I go hacking away, just wondering if anyone can provide guidance or thoughts on the matter?

On a similar note, bodies of water (eg Lake Manchester, QLD, Australia, image further below) there is a lake with the reserve is drawn around it. It seems like it would make more sense if the lake was placed inside the region (no border) or the lake and land/reserve borders were snapped together?

Thank you for your time

Rob

https://www.dropbox.com/s/qi9vt53aq1k7gvj/road%20corridors.JPG
https://www.dropbox.com/s/f905gp1b8efx4pu/Lake%20boundaries.JPG

turepalsson · 2018-08-31T06:11:58.000Z

To make matters worse, the national park is also tagged natural=wood, making it look like there’s a wide clearing around the road which, as far as I can tell from Bing, simply isn’t the case. Unless someone comes up with a good argument why we’re both wrong, I’d say: hack away!

(Maybe ask in the Australian forum, too?)

R0bst3r · 2018-08-31T06:16:23.000Z

Hi Rob, welcome to the forum.

In the 1st case I would keep that mapping style, because it may help in future to make edits more easier. To split polygons on roads is often a necessary step. I think also that roads (lines) and areas should not use the same nodes.

On the 2nd case I would agree. Didn’t see any reasons why to keep the gap. Both are areas and in reality there may be no other landuse in between. ???

TZorn · 2018-08-31T09:19:07.000Z

R0bst3r:

In the 1st case I would keep that mapping style, because it may help in future to make edits more easier. To split polygons on roads is often a necessary step. I think also that roads (lines) and areas should not use the same nodes

I think we should differ a bit. Unfortunately, that multipolygon mixes two different objects. For once it maps a natural=wood area. For that one it might make sense to split the multipolygon in chunks, making it easier to cut out other features as lakes, clearings or even roads running through a well cut line in the wood. The second feature is the national park (boundary=national_park, leisure=nature_reserve, etc.). The former is a physical objects (here be trees), the latter is an administrative feature and it should enclose whatever is defined in the national park declaration. My gut feeling is that roads a not excluded there, but who knows.

I would advise to separate the current multipolygon in two for the physical attributes and the national park boundary.

https://www.openstreetmap.org/relation/306431#map=12/-28.1680/153.2675

nevw · 2018-08-31T09:44:33.000Z

I would expect that the protected area boundaries that have been mapped as they are gazetted by the datasets that have provided by state and federal authorities are not altered except by later updated gazetted boundary data. The gazetted boundaries don’t necessarily follow the current road, river or water lines and may be instead based on countours or land parcels or other considerations we are not aware of and should not be conflated. I have noticed a great many of the gazetted boundaries of protected areas do not include roads or strips of future different infrastructure and often these roads or waterways have entirely different management and protection. As later gazetted data becomes available to update the areas it is much easier to manage if mappers have respected the gazetted data. It is often necessary to untangle roadways, steams, landcover type edits that have been merged with the gazetted boundaries when updated gazetted boundaries become available.

I think that a boundary of a national park would normally be expected to be tagged as natural=wood if that is a good description of the land cover. If a mapper wishes to spent more time and diligently map the reserved area as well as asdjacent areas as one or more polygons encompassing all the natural=wood areas that is a good improvement to the map but does entail a lot more effort.
Some mappers prefer to map and tag the gazetted boundaries and adjacent areas as seperate entities that are naturally wooded and that is an equally aceptable way to procede and also helps to keep the polygons to more manageable sizes.
I object to people changing the gazetted boundaries just to pretty up the map.

RobNicholson · 2018-09-02T04:04:21.000Z

Thank you all for your opinions.

I am fine with the multi polygon objects to remain if they are part of the gazetted data set. The map ‘prettiness’ was more of a secondary aspect. The main concern was management and editability of these corridors when trace data supports the road needing to move. If the road is moved should the corridor be also adjusted? It would seem strange not adjusting the corridor/national park boundary as the road would be driving in and out of the wood/national park, wouldn’t this cause confusion with end uses and other mappers? Not trying to make a mountain out of a mole hill, just want to make sure I am doing the right thing for future edits.

In the second example I think we all agree that the water body should be ‘inside’ the outer object (not the outer object having a cutout for the water body object to fit into, leaving a border/void)?

Thanks again

nevw · 2018-09-02T10:27:28.000Z

From your image, the road should be aligned to the satellite imagery and the gps traces.
I would leave the gazetted boundaries of the protected areas and accept that it doesn’t align with other features as expected sometimes and hope that future updates have better resolution and alignment with existing roads. The protected area boundaries are quite large and when new data becomes available each year or so the usual method is to merge the new boundaries into the map and replace the old ones and it is not really practical to adjust them to physical features on the ground. But if you find that reasoning is not suitable to your ideal, I expect that no one will object to you making minor adjustments as you are suggesting to align parts to your liking.

In regard to Lake Manchester:
I would have a look at the area in the OSM https://www.openstreetmap.org/relation/8242205#map=15/-27.4782/152.7681 and click on the last editors name and send him a message to discuss the area or just send him a link to this forum query so he can see what is being discussed.
I expect that he has left all the gazetted national parts boundaries as they are, then made other polygons to cover the entire wooded area/s. I expect that he has traced the actual waterline from the most suitable satellite imagery and that has left the gap which is likely to be ground or sand. The gap may grow or recede as the water level changes over the years but it is likely the tree line will remain where it is now mapped. There are a few sections where the tree cover overlays the surface water where streams enter the water body.

You could split the wooded boundary at the southern end where there is a gap in the wooded area and then draw a new way across the gap. You could then select the 2 outer ways to form an outer boundary and the 2 ways of the water polygon and then create a new multipolygon relation. The water has the inner role and tag the relation as natural=sand. You would need to adjust/fudge the boundaries so there are no overlaps.

Most mappers just draw the wooded areas and make an inner where the water bodies are and ignore the sand or ground gaps between the two.
I expect it is just a personal preference in how you prefer to map and I see both methods have merit.