> Has anyone seen something similar? Presumably this could happen to
nodes generally, there is no reason to think amenity=post_box is a factor.
Exactly that pattern no - but occasionally new users manage to drag
nodes by accident.
> Is there any way to identify features which have moved by more than
whatever distance might be considered "normal" for someone correcting a
previously incorrect position? This might be key to further
investigation and correction.
Yes - https://www.openstreetmap.org/changeset/81021329 is an example of
someone doing it. I'm not sure what software they're using though;
you'd have to ask. The mapper who added the comment there is I think
German, but I've had plent of conversations with them in English.
> I can provide the node and changeset numbers if anyone wants to look
into the details and perhaps can spot a pattern,
That might be useful so that someone can have a look. If you don't want
to post anything publicly you could perhaps just mail me (or anyone else
who wants to have a look) rather than post it forever on a public
mailing list.
> There are some philosophical question here: which features are
"allowed" to move and by how much? Natural features probably shouldn't.
They do - a bit. For example, while lowland waterways are normally a
pretty good match for OS OpenData StreetView (which is from some time
ago now) often their upload counterparts have changed quite considerably.
Best Regards,
Andy
On 15/02/2020 12:29, Dan Glover wrote:
If there's a better place, please direct me appropriately...
I've been using Robert Whittaker's Post Box tool to help fill gaps and
fix anomalies in the CT postal area. I think I've now found a pattern
which leads to "ghost" entries in locations where there has never been
a post box and leaves the actual post box either unmapped or with a
new node. I have three examples where the general scenario seems to
have been:
1. Mapper "A" creates a node with amenity=post_box. Other details
such as reference and collection time may or may not have been entered
at this point.
2. Time passes, possibly with edits to the node, but no change of
position.
3. Mapper "B" does something apparently unrelated. In the examples I
have seen it involves multiple ways/nodes, though not necessarily vast
numbers.
4. The node created at (1) is re-positioned in a fairly random manner
as part of the same changeset.
5. [possibly] Mapper "C" spots the missing post box and creates a new
node for it. The node from (1) is still "out there", in one case it
was 1.3 km from the original (correct) position.
Note: it transpires Mapper "A" in the three examples is the same
user. Three different "B"s.
I suppose the first questions are:
- Has anyone seen something similar? Presumably this could happen to
nodes generally, there is no reason to think amenity=post_box is a
factor.
- Is there any way to identify features which have moved by more than
whatever distance might be considered "normal" for someone correcting
a previously incorrect position? This might be key to further
investigation and correction.
I can provide the node and changeset numbers if anyone wants to look
into the details and perhaps can spot a pattern, The edits are by
three different users on widely spaced dates and the iD versions are
all different. The most recent example was in September 2018, so it's
not likely the mapper would remember anything.
Robert's tool shows the distance between OSM node and Royal Mail data,
which is how I found one of the examples - but it is "normal" for RM
data to have discrepancies, sometimes fairly significant. The other
two had relatively minor offsets and were picked up through "local
knowledge" - but analysis of old/new position could have highlighted
them. Unfortunately post boxes do get moved whilst retaining their RM
reference but I'd expect that to be done in OSM by creating a new node
and deleting the old.
There are some philosophical question here: which features are
"allowed" to move and by how much? Natural features probably
shouldn't. Man-made ones are probably something new when they do
move. Boundaries, however, are subject to revision, roads and
footpaths get re-aligned. Also what's an acceptable margin for a
correction?
Dan
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