[Tagging] Sewage, tailings, and evaporators

Kevin Kenny kevin.b.kenny at gmail.com
Sat Jan 9 19:57:18 UTC 2021

On Sat, Jan 9, 2021 at 1:41 PM Brian M. Sperlongano <zelonewolf at gmail.com>

> For the case of sewage and tailings at least, I'm thinking that these are
> quite discernable from waterbodies.  It should be pretty straightforward to
> come up with a gallery of examples as to what they look like on imagery and
> how they're characterized.

Frederik has a point. I'd be hard put to tell in
https://kbk.is-a-geek.net/attachments/20210109/Tahawus.jpg what is natural
water and what is tailings - the mine is right on the river. And I'd have
an even harder time if the mine has been abandoned for over a century, as
at https://kbk.is-a-geek.net/attachments/20210109/Surebridge.jpg. (I still
won't drink from a couple of the streams in the latter image! The water
tastes foul and is widely suspected to be contaminated with heavy
transition metals, even after all that time.)

Then again, mapping waterbodies from aerials around here is harder than it
looks. Many orthos show either ice or mats of floating vegetation, both of
which can be hard to distinguish from adjoining land. To do a really good
job, you need to compare imagery from different seasons.

Nevertheless, I'd personally be perfectly fine with tagging 'natural=water'
on any of these objects if mapping from aerials and fixing it when better
information is learnt.  It's no worse than other mistaggings I've seen
arising from misinterpretation of imagery. I don't think that means that
sewage farms, tailings pools, or spoils evaporation basins (
https://kbk.is-a-geek.net/attachments/20210109/VischerFerrySpoilsDump.jpg -
when dredging is active, the basin is indeed flooded; the orthos caught a
dry time) have to remain `water` once the mapper knows better, even if it
makes sense to tag them that way initially. It's no worse than mapping
`natural=water` and discovering that the imagery you were working from
happened to be captured during a flood. (Don't ask me how I know about
_that_ problem!)

I personally use orthoimagery only to supplement a field survey or to
sanity-check an import, not as a primary reference. If I see something on a
survey or discover it in an import, I may use imagery to capture
approximate geometry, but generally I want corroboration that the object
I'm mapping exists and is what I say it is. (I don't complain that other
people armchair-map - I just don't do it myself because of this sort of
73 de ke9tv/2, Kevin
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/tagging/attachments/20210109/f66258d7/attachment-0001.htm>

More information about the Tagging mailing list