Re: [osm-hu] Questionable edits around Alsószölnök

[Ferenc Veres]

It's difficult to review history of these areas (now), so the old CLC 
import may not be related, but around 2012 we imported many landuse data 
from EU's CLC database. (Just like many other countries did!) That 
indeed created landuse that didn't cover the actual BING imagery well - 
it's because different age and source of the CLC data and human errors 
in creating that data. After importing more and more areas, we decided 
this is creating useless data and we stopped. (We used different levels 
of automatization vs manual correction. But the best result came from 
simply not using CLC at all! I agree with you there.)

Regarding MultiPoligons: we use a GIS-like approach here, where this 
certain data type (land cover and land use) is about to form an 
underlaying layer for the map, fully covering the world. Everything else 
will be drawn over this layer of 100% cover. E.g. a street may be in a 
town, forest, farmyard, or even on water if it's a bridge, but there is 
always some ground base for the objects. Since OSM does not have this 
approach defined (but nothing is making this impossible or bad - 
basically the whole map (and every map) is like that!), we sometimes 
have hard time to decide what objects are part of this "land use and 
land cover" (e.g. recreation ground, park) or whether the area should be 
subtracted from the larger area (multipoligon inner way).

(If not subtracted, it's up to the render engines to figure out which of 
two overlapping objects is up and which is down - which is bad data design.)

Thus we are not leaving empty 10 meters space between these elements, 
like you do here:

https://www.openstreetmap.org/way/579139233#map=17/46.91764/16.19432

(In this example the surrounding ways are not part of neither the forest 
or the farmland, usually we would adjoin areas, so that the roads go on 
the farmland (or forest, which covers the reality best). Just like ways 
running within the town are not left alone outside the town's polygon.)

That requires millions of adjoining polygons - which would mean millions 
of overlapping way objects. So the use of multipolygons is just a 
logical optimization: every edge of this network will have only one line 
object. Simple as that.

No need to draw very long lines over other very long lines over and over 
again, just draw everything once and use for two object's adjoining edge.

Regarding difficulty in editing:
1. Editing tools should make this easier.
2. I agree that very big objects should be split and are bad.
3. Human errors don't make this method bad. It's a method that can be 
learned and used and works very well if used right. (And please read 
back to point "1." for beginners.)

Regarding "vandalism": I think the guys refer to the method of deleting 
big number of objects and creating them from scratch. We usually prefer 
EDITING existing objects to throwing them away (and AFAIK this is basic 
OSM rule).

I didn't see the original landcover here, but if it's a raw CLC import, 
completely deleting it may be reasonable. (Or over other bad edits, yes, 
there is a place for such remake.)

Regarding Alsószölnök: I found you draw adjoining farmyards as separate 
items, I don't find this necessary.

For example this:

https://www.openstreetmap.org/way/579154541#map=18/46.89294/16.18852

and to the North and South directly. This year they may be planted 
different weeds but another year another species may change their look, 
may make all the 3 identical. I think areas should be kept as big as 
possible but within a few km limit.

And in general, I think editing should respect the work of those who 
regularly edit the area. Unless you fix plain errors, just changing 
"editing style" is not reasonable. And I don't think there is "Hungarian 
editing style". Even all these examples are similar:

https://wiki.openstreetmap.org/wiki/Multipolygon_Examples

The most specific example:

https://wiki.openstreetmap.org/wiki/Multipolygon_Examples#Farmland_adjacent_to_forest_and_farmyard_adjacent_to_lake_.28Adjacent_multipolygons_and_adjacent_inner_areas.29

Best regards,
Ferenc




2018.08.24. 10:16 keltezéssel, Gergely Matefi írta:
> Dear fellow Mappers,
> 
> JM82 provided a long answer to our critics in a changeset comment:
> https://www.openstreetmap.org/changeset/61775261
> 
> I suggest to follow the discussion in this forum due to the wider 
> audience. I encourage you to use English at this thread to allow JM82 to 
> join to the discussions.
> 
> Regards,
> Gergely
> 
> 
> Kedves szerkesztőtársak,
> 
> JM82 írt egy hosszú választ a korábbi kritikáinkra, javasolnám a vitát 
> ezen a fórumon folytatni. Lehetőleg angolul írjatok, hogy JM82 is 
> csatlakozhasson.
> 
> Üdv,
> Gergely
> 
> I would now like to comment on the allegations made here regarding this 
> changeset as follows:
> In the OSM-Inpector 
> (https://tools.geofabrik.de/osmi/?view=areas&lon=15.8752&lat=46.9491&zoom=12) 
> there are regular errors with multi-polygons in this region, which 
> unfortunately do not only affect this one CS, but the entire region 
> around Szentgotthard. MPs are not closed, are faulty and often 
> incorrectly set.
> At this point, I would like to make a reference to the German OSM Forum, 
> where (exactly two years ago) exactly this problem is being discussed on 
> an ongoing basis. It is particularly bad in this region of HUN, as here 
> often every single field, every meadow is created as MP, which is also 
> not a member of a real MP relation, but simply placed as MP alone. This 
> is according to the wiki of OSM, which also exists in English, not the 
> intention of MPs and they should not be used like that either. Why and 
> why does the HUN community shun here and describe it as a "Hungarian 
> mapping style". In addition, these MPs / landuse areas do not correspond 
> to the aerial photos that are available via OSM today, but more on that 
> later. In short, the timeliness is not given.
> That's one reason why I've deleted some MPs and replaced them with 
> simple, usually much smaller, land areas.
> 
> It should also be noted that the OSM data in this region appears to come 
> from (semi-) automatic imports that were carried out many years ago. 
> This leads in this context also to the problem of MPs in general and 
> their use.
> Another reason, in some areas of the area, is that MPs are already so 
> large (in terms of both surface area and number of members) that editing 
> has become almost impossible for some editors. But that's exactly what 
> OSM lives by: the timeliness of the data and its change! Landscapes are 
> changing, even in West HUN, land uses are changing (fields are turning 
> into meadows and vice versa, towns are getting bigger, new buildings are 
> being added).
> Smaller land areas are editable with all editors, changeable and so on. 
> Numerous MPs in this region are just that, because they have grown so 
> big that nobody can handle them.
> The next reason for my changes was that the JOSM editor constantly 
> points to errors of MPs in this region as part of its review: non-closed 
> MPs, interchanged inner / outer relations. These are exactly the errors 
> that come along because of this excessive use of MPs, which - due to the 
> local landscape, should by no means be set in this way. For this reason, 
> I have also begun some time ago to bring the MPs in their extent as well 
> as the number of their members to a reasonably workable measure. 
> Furthermore, I have corrected many Landuse tags for the existing aerial 
> images and erwweitert.
> Likewise, for the sake of completeness, I would like to point out that I 
> am not against MPs per se, but they try a) to avoid, b) use sparingly 
> and c) make changes if I am
> Rather, OSM in this region was apparently imported semi-automatic years 
> ago and no one has taken this data, because these are not only often 
> outdated (testing via Bing, geoimage.at <http://geoimage.at/> maxRes or 
> other image service providers), but also often inaccurately mapped. 
> That's obvious
> 
> Another reason was the addition of landuse areas. As you can see 
> clearly, I have supplemented numerous landuse areas (mostly fields, but 
> also meadows), since the quality and the mapping style in this region is 
> often catastrophic: over a few square kilometers simply arable land is 
> stretched over it, with no aerial picture in it Are to be reconciled.
> 
> To the individual points further:
> "Making huge changes with no comment is a terrible thing to start with, 
> and the fact that they are mostly simplifications".
> OSM is a community, act like you are trying to be a member and not a 
> destructor of it. "
> I have not made any major changes in this CS by far, as can easily be 
> understood. To change a MP or parts of it can hardly be called such.
> 
> Multipolygon-based landuse structure is adopted and preferred by the 
> local OSM community and many other mappers follow that mapping style 
> like this is a vandalism that does not make sense in the future. "
> What is the meaning of mapping every single land area as an MP? The 
> effort only increases, there is no recognizable added benefit of this 
> measure. Only because I do not map land areas as MP - without worsening 
> the informative value of the data - is that in your opinion vandalism? A 
> strange, almost incomprehensible definition of vandalism.
> Where did I make systematic changes here? I've added additional Landuse 
> tags and overhauled existing ones that did not fit together with the 
> aerial photo altogether or not at all. That is verifiable by means of 
> appropriate aerial photographs.
> 
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