[josm-dev] Move-happy JOSM - a concrete example

[Dermot McNally]

It's been at least a few hours since I last warned of the dangers of a
move-happy JOSM, so here's a real world example that happened to me
last night.

I began to see broken rendering on Lough Derg, a lake in Ireland:

http://www.informationfreeway.org/?lat=52.911668677334255&lon=-8.368346693600273&zoom=11&layers=0B00F000

Opening the thing up in JOSM revealed the likely cause - an open piece
at the southern point of the lake (which is also where the river
drains it). I knew that it hadn't been like that when I mapped it, so
I concluded that it must have become broken during the 0.5 upgrade
(it's quite likely that the missing "former segment" was shared with
the riverbank).

Anyway, since I couldn't quite get the hang of which special key and
click combinations would allow me to close the circle in the new JOSM,
I just drew what I needed in Potlatch and merged the ways in JOSM.

I didn't pay too much attention to the what-you're-about-to-upload
dialogue, and when I pressed OK essentially every node on the lake
re-uploaded. My conclusion - when selecting the lake's bounding way, I
had managed (without realising it) to shift it ever so slightly. The
change is unlikely to be significant (traced from Landsat), but this
is a very scary behaviour, don't you think?

Dermot