When I first started mapping out my town in 2016, there wasn’t a definitive overlay like OSMUK Cadastral Parcels to align everything to. I took some GPS traces from my phone and worked from that.
When Cadastral Parcels came about, I saw my GPS alignment was slightly out and rather than try and move the whole of Bexhill - I just said “close enough” and carried on.
Recently a new mapper has started adding extra detail using Cadastral Parcels (rightfully so) which creates overlapping issues when the rest of the area is on the wrong offset.
I’ve done a test using JOSM to try and move the 250,000 nodes needed to fix the alignment. It does seem possible, but rather than going ahead and doing it, I thought I’d ask here about best practice?
I don’t know about best practice, but I would highly recommend you contact the other local mappers when you plan your big move. So that you don’t end up with making edits at the same time and producing a ton of conflicts.
It should be possible to break the task in a few smaller changesets, and clean up manually afterwards. I did something like that in Nuuk, Greenland, which is not a big city and not very densely mapped.
Is there a limit for maximum changeset size using the API? If not, you could try everything at once and see what happens.
Yepp and it’s a lot lower than 250’000 (currently 20’000 iirc), which is the largest technical issue with the proposal. If some thing goes wrong you’ll have a big mess of moved and not moved nodes. See SimonPoole's Diary | Handling failed uploads properly | OpenStreetMap for more on this.
JOSM will split the upload automatically, but as noted above that is more of an issue than a solution. I would manually select smaller areas and do those one by one.
Then: is this even necessary? A link to the location in question and one of the problematic areas would be helpful.
(Und der Versatz von weniger als einem Meter ist aus meiner Sicht absolut tolerabel! Insbesondere, wenn man bedenkt, dass die Daten vorher auf Basis der (damals anscheinend etwas anders eingepassten) Katasterkarte eingetragen wurden => Node: 8753115931 | OpenStreetMap )
Not to mention that 1m is in the same order of magnitude as the continental drift over a decade ~25cm (lets be happy that it isn’t a place in Australia).
IMHO I would use the better source for new and updated stuff and simply fix any conflicts when they actually arise.
You know in an action movie where the hero shoots the other guy right between the eyes? That’s preciseness.
However, making sure he shot the bad guy and not the innocent bystander is really important. That’s accuracy.
They might be 1 metre off from each other, but only 0.5 metres off each from reality. Or they might be 14-15 metres off from reality.
In lots of places, aerial imagery is taken as more accurate than satellite imagery. However, as the software that processes the aerial imagery doesn’t have a perfect model of the planet, it often has issues dealing with things like very steep ground, powerlines, tall viaducts and tall buildings, meaning that the shape, size and position of those objects is distorted.
I think our objective in trying to map a world that is constantly changing anyway should be that things are accurate (most importantly to other nearby objects) and representative (not much use in pressing everything together if it produces a map that can’t be read or understood), not precise.
Here: Node: Glenflesk (52245592) | OpenStreetMap some objects are off by 12 metres and the community considers the black and white photography from 2012-2013 to be the most accurate.
