[talk-au] Tracks flagged as missing from government data

[Little Maps]

 Andrew, thanks for the super fast reply, and for the overpass query which
I'll cut and paste from! A few thoughts…

AH: 1.98% of tracks have public vehicle access and 8.7% of tracks have no
public vehicle access (of all tracks). So where we know the vehicle access
then 18% are public and 81% are not public access.

This makes sense. To date, in Vic at least, most mapped tracks are on
public land or on the public road network (the opposite trend may exist in
outback areas). So existing mapping is strongly biased to public tracks,
and access tags have mostly been used to indicate restrictions.

I just re-read the Aus tagging guidelines and it has a similar emphasis. It
explains how to add access restrictions but doesn't say that public access
isn't a default on tracks or that access=public is a worthwhile tag to add.
I'll put together some draft text to add to the page and will circulate for
comment in a day or two.

AH: In my view, data consumers should treat incomplete access/motor_vehicle
tags as no access because I'd rather it miss out on a potentially available
route then route down a private track, but that's a decisions for each data
consumer.

I have a different take, but I think you'd be happy with my ideal router.
It would give me 2 options: (1) use all available tracks (public + unknown)
vs (2) only use known public tracks. Given how few tracks have an access
tag, most users would default to "show me all of them", but they'd have a
choice. Globally, only 3.8% of tracks have an access tag: 20.7 million of
21.5 million tracks don't. Any app that only used known public tracks would
be viewed as crippled by users and would go broke. The market would force
developers to show all tracks, regardless of their personal intentions.

Luckily for me, the strong bias of osm mappers for mapping public rather
than private tracks is why routers that do assume that access is public
unless indicated otherwise actually work pretty well in Vic (prob not in
central Aus). As more and more private roads are added we can expect this
convenient correspondence to fall apart though. That's why I was so
concerned about the Challenge adding lots of private tracks without having
an access tag on them, as it will be the first major influx of untagged
private roads to Vic.

AH: So I can understand, do you think we should have a default value and
mappers should not set the access tag if it's the "default"?

A question: I don't understand how the "default value" approach differs
from Joe's suggestion, which as I understood it, was that if access is
assumed to be no, then he wouldn't have to bother adding access tags (inc
access=unknown) when doing armchair mapping. Doesn't this have the same
outcome as a default position of not needing to add a tag? However, despite
the fact that I don't comprehend the distinction, I don't think it matters
a great deal.

If there was a discussion to try to reach consensus on whether we should
assume that access=yes or no when there is no access tag, I would take one
of two positions: support access=yes or continue to make no assumption
about access. I wouldn't support an assumption that access=no for the
reasons I've described above. I think I'd probably just take the long term
view and say, avoid the debate and tag everything.

By analogy, until recently the Aus community took the view that there was
no need to add paved surface tags on roads and only unpaved tags needed to
be added. Paved was taken as the default value. As lots of roads had no
tags it was impossible to know which were actually paved and which just
hadn't been tagged. Same problem to here. Fortunately, heaps of mappers
added paved tags anyway, which enabled us to get to the stage this year
where virtually every road down to tertiary level across the whole country
now has a surface tag (except in Melb and Perth). Soon every unclassified
road in Vic will have one as well. Keep chipping away at the job is my
suggestion.

If we want to make progress on access tags, I suggest we need to discuss
loosening the restrictive (IMO) approach that we currently take to adding
access tags, which is to avoid adding them unless we see it on the ground.
That's unscaleable across Australia in any meaningful timeframe. I'd be
happy to support well-designed imports and challenges that used reputable
datasets that contain access restrictions (e.g. Vic transport data; Dry WO,
MVO, seasonal closures, etc.) and (perhaps) to use these datasets to
indicate access=public, which is where we have the biggest gap in our data.
This way we could make much faster progress. We'd make some mistakes but
the system is iterative and editors continue to do an awesome job to refine
an amazing map.

Ultimately, I'm with you in that, we can develop the best map if we
accurately tag access everywhere. Thanks again, Ian
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