Actually mapper mentions would be at least as useful but likely not really feasible due to the extreme abuse potential.

Note what you suggest, namely to automatically add a back-referencing changeset comment is much more obtrusive than the github feature which just silently adds a back-reference without a notification.

A quick update: the challenge now has a more elaborate description:

This challenge consists of islands which have overly sharp angles or are over-simplified. Check all available imagery before editing the islands. Bing may be offset, so only fix a task if you have calibrated imagery of the area. Please skip tasks where imagery is not available. Please familiarize yourself with the proper alignment of coastlines, this information can be found on the OpenStreetMap Wiki.

This is not quite correct, tasks also exist for islands with fairly smooth outlines so their thresholds are fairly off but it explains how they produce their tasks.

And those working on the tasks now seem to be more selective in what they change, there are now nearly as many new tasks marked as false positive as there are as fixed.

Overall this is now mostly sad in terms of waste of ressources. All of these problems could have been avoided if they’d have discussed their plans beforehand. If half the tasks you look at turn out to be bogus that is just not very efficient.

So a policy for organized editing would not only be in the interest of OSM, it would also be in the interest of those organizing such edits. ;-)

Editing has resumed, some of the changeset comments have been replied to, including the admission that this is an organized effort but still pretending this to be a normal group of regular OSM mappers and not telling who instructed and is paying them.

Yes, agreed. And @mvexel already indicated he does not want Maproulette to be used for shadow mapping activity and i assume there will be changes to prevent such abuse in the future. And if there is further need for more thorough QA for the challenges posted there would be options for that too (like for example a grace period between publishing a challenge and it becoming available for mappers to work on which can be used for evaluation).

I have my doubts if without a clear mandate in form of binding rules volunteer administrators can do much good here but of course Maproulette can introduce such rules independent of the OSM community as a whole and if they work well this might serve as a basis for developing a broader general policy.

In all fairness one other thing needs to be said - that a contributing factor for the problems of this challenge is that we still use totally unsuitable images for mapping from Bing and Mapbox in many parts of the world and editors do not even give a warning not to. This would be very easy with Bing (Capture date in the metadata is 1/1/1999-12/31/2003 or 1/1/1999-12/31/2014), somewhat more complicated with Mapbox. We cannot and should not forbid using these images but a clear warning to any mappers doing this from the editors would be a big advantage.

@mvexel - Since massive work on this challenge by the mappers mentioned above started before you posted the link in public the challenge obviously has been used as exactly the kind of shadow activity you did not want.

I am not really inclined here to try finding out details about this via PM from a user who obviously wants to hide his identity with a user account specifically created for this purpose.

To me this all just emphasizes my initial impression that we need enforceable regulations for this kind of large scale organized mapping activity.

In this particular case, I would get in touch with the Challenge creator (there is a link in MapRoulette to their user profile) and ask them to comment here.

I see no way to determine who created this challenge within Maproulette.

If I were to shut down this Challenge, What is to stop them from just scrolling along the coastline looking for islands to fix in the same way they are doing it now?

Actually that would be a great improvement over what happens with the challenge. Right now mappers tend to edit only the island in question before moving to the next one in a completely different area and not look around and edit more stuff in the same area. Look for example here or here where there is lots of stuff to fix and improve around (the second one is near to what is probably the largest group of unmapped islands in Europe). Without the challenge mappers inclined to fix inaccurate islands would select an area they are interested in from the start and would also learn further about the area while working on it. This would be much better.

I have already linked to two commented changesets (where i did not yet know this is a Maproulette challenge):

osm.org/changeset/47030425

osm.org/changeset/47032866

Today i made another comment:

osm.org/changeset/47195925

And yes, of course these are different from a fully automated edit, my title is a bit of a clickbait obviously.

@Jochen - we don’t know yet how this challenge was created so it is somewhat premature to draw far conclusions but obviously you cannot identify potentially misaligned islands without external data unless you simply put all islands in the challenge which does not seem to happen here. This makes it very different from tools like OSMI or Osmose which focus on internal inconsistencies in the data.

The primary problem is here definitely the person who created the challenge, instructing mappers to align the highlighted island to match imagery which is just a plain wrong instruction here misleading mappers into doing what they should not do (namely aligning the island to what they see in the images without knowing the area, the imagery or the previous mapping work done).

The secondary problem is that those running Maproulette have apparently no system in place to ensure even the most basic level of quality on the challenges posted. At the same time and in contrast to the wiki (which you mentioned for comparison) others have no way to fix problems with the challenges and remove misleading stuff.

And after that there is of course also the problem that some mappers let themselves be lured into following the faulty instructions given and damage the map in a misguided attempt to improve the map. But the responsibility lies with others, you cannot just put a mapper into the loop and then put all the blame on the mapper while you hide in anonymity.

It seems by the way this challenge has been flying under the radar in Maproulette - you don’t see it on the metrics or using the search function, you need the direct link. I wonder where all the people working on this got the info from…

It should be noted that what Bing offer is by far not the best available imagery here - even when ignoring the better black-and-white image offered by Mapbox in this case. Even though the classification of the road is not really identifiable from images, often not even when they are very high resolution, it is generally advisable to have some image as context when you map in an area where you lack recent first hand on-the-ground knowledge.

This is especially important for parts of the world where roads might be seasonal - like winter roads over a frozen lake - not really an issue in southern Sweden but definitely a possibility elsewhere in Scandinavia.

There is no universal recipe to fix this kind of problem. There are many different kinds of mistakes that occur in broken multipolygons and each of them requires a different approach.

Things that are helpful usually with with riverbank polygons:

• make the individual polygons small - don’t make the mistake of fixing things by merging everything into one big polygon.
• decide on which area your polygon is meant to cover along the river
• throw out all members outside this area
• throw out duplicate members (which are in the relation several times)
• assemble a closed outer ring, if necessary drawing new ways or splitting ways
• add all islands within as inner rings
• make sure all tags are on the relation and none are left on the member ways (unless they apply only to them)
• create additional polygons using members previously removed as necessary

This is all a matter of exercise and training but even with a lot of experience this is still tedious work.

But that is not a city in terms of the meaning of place=city in OSM.

In general having settlements of this size not mapped beyond a node is nothing rare in OSM. It was not rare in Europe 5-7 years back either.

Ich meinte das mit der Konvergenz für kurze Distanzen und nicht für lange. Das hängt natürlich dann auch davon ab, was für eine Interpolationsvorschrift man für die Höhenwerte verwendet.

Anstatt den Radius zu variieren könnte man übrigens auch die Höhendaten vorher filtern, hierdurch ließe sich der Einfluss von Rauschen und anderen Artefakten in den Daten vermutlich besser reduzieren als durch einen größeren Radius.

Ein anderer Ansatz wäre, nicht mit einem festen Radius zu arbeiten, sondern für jede Richtung so weit weg zu gehen, wie notwendig ist, um eine bestimmte Mindest-Höhendifferenz zu erreichen.

Hübsch.

Zwei Überlegungen dazu:

• man könnte versuchen, bei der Berechnung als Nebenprodukt auszugeben, welche Sattelpunkte vermutlich falsch platziert sind, also wo der Punkt im Relief deutlich erkennbar nicht an einem Sattelpunkt liegt.

• zur Maßstabsabhängigkeit: Wenn man die Richtung eines Sattels als Funktion des Abstands, in welchem die Richtung ermittelt wird, sieht, konvergiert diese Funktion bei eindeutigen Fällen (korrekt platzierter Punkt in Gegend mit starkem Relief und guten Daten) wohl im Allgemeinen für kleine Abstände gegen einen bestimmten Wert. Bei hohen Zoomstufen wäre es vermutlich sinnvoll, diesen Wert zu ermitteln und zu verwenden. Andersherum könnte man auf diese Weise auch erkennen, wo die Richtungsbestimmung sehr unzuverlässig ist (Wert der Funktion schwankt stark oder weist Diskontinuitäten auf).

Thanks for the writeup and the data.

To me with the two seats that were up for election an interesting observation is the frequency of the different combinations for first and second positions. Even though this is not how STV works (i.e. you do not have two votes for two seats) it still gives an impression what voters would consider the most desirable candidate pairs - or in other words: who would be elected if everyone voted like you.

Obviously Frederik-Kate and Kate-Frederik were the most common combinations. The next most frequent combinations were

• Frederik-Guillaume (not far behind the two top combinations)
• Kate-Darafei (much less frequent)
• Frederik-Darafei
• Kate-Guillaume

The all new candidate combinations (Guillaume-Darafei and Darafei-Guillaume) were equally popular and together as frequent as the last two in the list above.

What you describe is probably in large parts an experience many people with a background in classic cartography share.

Regarding the purple boundaries - this is something a lot of people are dissatisfied with in the standard style, but it is not easy to change. But the good thing is of course that not all OSM based maps have purple boundaries so anyone who does not like them can easily find a map without these.

I don’t think in map design there is a clear division between conventional cartography and OSM regarding what works well design wise and what does not. The main difference are the circumstances - the lack of a central authority, the world wide coverage, the heterogeneity and generic nature of the data and the need for real time updates in rendering for example. In my experience much of the difficulty of conventional cartographers in ‘getting’ OSM is related to the difficulty to comprehend these differences and what they mean.

That looks interesting but if i understand it correctly you are inferring the hydrographic network from relief data at least initially without any confirmation that a waterway actually exists there.

May i advise a bit of caution here. If you cross check with imagery afterwards that is fine (and having a pre-generated network to start with is probably very useful). But without any visual confirmation this can lead to pretty large errors like here:

http://mc.bbbike.org/mc/?lon=142.895006&lat=52.311073&zoom=14&num=3&mt0=bing-satellite&mt1=mapnik&mt2=mapbox-satellite

Even in areas where no high resolution imagery exists this can be avoided by using available images.

World map projections with a split not at 180 degrees longitude - as BushmanK suggested - are a special difficulty - better to start with the basic version here. That should not be a problem - unless your rendering setup really sucks.

Regarding the map itself - looks like quite a clear case of regional bias. The extreme emphasis on sub-saharan Africa is most obvious - but even apart from that this is clearly not a map showing the most serious objective needs for mapping across the world in the past years.