[talk-au] Missing streets in Sydney
slhope at gmail.com
Thu Sep 15 06:45:30 BST 2011
On 15 September 2011 10:49, Ian Sergeant <inas66+osm at gmail.com> wrote:
> Of all the ways in Australia, less than 50% have source tag for how the
> location/name information was derived.
Is that the most recent version, or the first? Also, it may be higher
than that. Did you you check the change sets? Some people put their
source comments on the changeset, not the individual ways.
> Of those that do, around half indicate some form of imagery was used as the
> source (it seems that we are a country of tracers :-).
Were they traced originally, or just updated later when nearmap first
came available? In the area I know best, pretty much every road got a
nearmap source tag within a couple of months of the nearmap imagery
becoming available. Do any editing with the nearmap imagery as the
background in potlatch, for example, and it added the nearmap tag,
whether you actually traced it or not. And there were people going
around tweaking the geometry of whole suburbs that already existed in
one session, and the whole lot would end up with a source= tag. All an
imagery source tag really means is "at least one of the changes done
to this item was done by somebody who either themselves or their
editing program decided a source tag was appropriate", not "this road
was traced from an image".
> Interestingly enough, around a quarter of ways traced from imagery are
> named, with no source tag indicating of how the name of the way was derived,
> could you say that at least some of these have been surveyed without being
> tagged accordingly? Or could you even think something more sinister?
When I started, we were told not to use a source tag for surveyed,
only for other sources. Almost all the original roads in my area had
no source= tag. And namespacing of source tags was never mentioned -
in fact there was a real push against namespacing any tags for a
while. I have myself named a bunch of roads somebody else traced
after a visit to the area - and I didn't change the source tag because
I didn't survey the roads myself, just look for their names. I didn't
put a source:name tag either because we didn't do that then.
However, I'd guess most of them were roads that had been surveyed and
named before, then had the positioning improved from imagery later.
Check what percentage of them have a version with the name before a
version with the source tag, if you want an idea.
> My conclusion - there is no way I can see in Australia to reliably construct
> a surveyed or traced data-set based on the tagged source information as it
> now exists.
I'd agree. Though if you were willing to take certain values as
defaults and looked at the history of each way, I think you could get
a good overall picture. But not a at the detail level you'd need for
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