Issues with Japan imports

Posted by bdiscoe on 3 March 2018 in English (English).

I’ve run my find_small_displacements program on Japan, and found some problematic imports with a large number of densely overnoded features, here are some:

  1. Bad import of natural=wood around Fukuoka. These were tightly spaced, yet also wildly inaccurate, off by as much as 80 meters and covering lots of non-wood areas, even covering motorways. I’ve reduced most of them, and aligned a few areas, but there’s lots more to align. The original upload was in 2010 with changesets like this one.

  2. Bad waterways, especially in Hokkaido and Kyushu, but also across the country; these are not just overnoded but also overtagged, consider this little stream near Taketa, Ōita:

  • KSJ2:COP_label=1級指定区間
  • KSJ2:DFD=流下方向不明
  • KSJ2:LOC=c03671
  • KSJ2:RIC=8909180118
  • KSJ2:RIN=軸丸川
  • KSJ2:WSC=890918
  • KSJ2:curve_id=c03671
  • KSJ2:filename=W05-07_44.xml
  • KSJ2:river_id=gb02_03671
  • layer=-1
  • name:ja=軸丸川
  • name=軸丸川
  • note:ja=国土数値情報(河川データ)平成18年国土交通省
  • note=National-Land Numerical Information (River) 2006, MLIT Japan
  • source=KSJ2
  • source_ref=
  • waterway=river


Issues with this little waterway:

  • Poorly aligned; off by 20-60 meters in all directions.
  • A large number of tags that belong on the changeset, not the feature; to its credit; this wasn’t a practice back in 2010 when it was imported.
  • Overnoding, using 1085 nodes for what is well represented by 40 nodes.
  • It’s tagged “river”, but is clearly a small stream.
  • “layer=-1” for every single waterway.

Also somewhat alarming, JOSM does not show all the tags (!?), the “KSJ2:” tags are present on the feature but do not appear in JOSM’s GUI. I could not find any option in JOSM to make these key/values show up! Perhaps a JOSM expert could weigh in, or I should file a ticket.

Comment from Viajero Perdido on 3 March 2018 at 20:40

JOSM seems to have a (hidden?) list of deprecated tags that it keeps under cover.

I’ve noticed (coincidentally today), while browsing my own work in achavi, that when I touch a highway to edit a tag, JOSM also removes two tags, geobase:datasetName and geobase:uuid. These are from old imports, and I assume they’ve been declared utterly useless - and thus removed without comment.

That would explain the “remove obsolete tags” or somesuch that I keep seeing in my command history. It’s nothing I’ve done knowingly.

Comment from Viajero Perdido on 3 March 2018 at 20:44

PS, it may be the SImplify command that removes those tags.

Comment from SomeoneElse on 3 March 2018 at 21:03

(re tag removal) JOSM, and some other editors, will remove some imported or previously set tags that subsequent discussions have suggested are best removed. See the comments at for example.

Comment from bdiscoe on 4 March 2018 at 00:07

Thanks Viajero and SomeoneElse, i tested it and that is indeed the case:

  • JOSM hides the deprecated “KSJ2:” tags in the GUI, although you can still see them with “View: Advanced Info” (Ctrl+I)
  • If you change anything about the way (say, removed the bad “layer=-1” tag) and upload it, then JOSM automatically removes the deprecated tags as well.

That’s a fascinating undocumented JOSM feature. I approve of it, although in this particular case, I’d argue that even more of the tags in this particular import could/should be removed, including: * “note” and “note:ja” which are absurd to have repeated on every single way. * “source_ref” which doesn’t tell you anything that “source” doesn’t already. * “name:ja” which is an identical copy of “name”; unlike some other countries, Japan’s OSM data has no issue of exonyms appearing “name” tags, so this is truly useless.

Comment from _yog on 5 March 2018 at 00:03

Japan has a lot of bad data due to imports.

There was the big road alignment project launched in 2015 that had a good success and helped cleaned a lot but I know I’ve been realigning, combining short segments and reducing the number of points on straight roads for the past 2 years around the Nagasaki region, and I’m far from being done…

The task is huge.

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