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:
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.
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:
- note=National-Land Numerical Information (River) 2006, MLIT Japan
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.