[Talk-us] Low-quality NHD imports

Kevin Kenny kevin.b.kenny at gmail.com
Fri Oct 13 14:06:08 UTC 2017

On Fri, Oct 13, 2017 at 4:53 AM, Christoph Hormann <osm at imagico.de> wrote:
> I think this is probably a good example for imports discouraging manual
> mapping.  If this data was not there mappers would probably meanwhile
> have added at least the larger rivers but with the dense network of NHD
> geometries with a lot of cryptic tags and all flatly tagged as
> waterway=stream it is quite hard for mappers to identify the larger
> rivers and improve mapping there.  Like here (NHD import on the left,
> newer manual mapping on the right):

What *should* have been done: artificial flowlines with shoreline should have
been 'river', most other should have been 'stream'. That would have worked
in most cases. But that's all water under the bridge (and people complain
that in initial mapping, I just cross roads over streams, and go back and
add the bridges and culverts later as time permits - usually it doesn't).

I remain unconvinced that importing or not importing has had any
significant impact on whether people improve the map manually.

NHD was never imported around here. I miss it. Only the most significant
rivers are in OSM. The lack of an import didn't motivate manual mapping,
except that at one point there was a project to map ponds (from a file of
point data). The result was a bunch of pond outlines that are pretty rough,
and confuse floating and emergent vegetation (common in our shallow
waters) with land. For that specific set, I find NHD more reliable.

Across the state line, NHD was imported in some neighbouring states.
There, I at least have the waterways in OSM. Are they any better or
worse than the few manually-mapped ones I have here? On the whole,
they appear to be better. There are some specific instances were
they're very bad. I don't see much maintenance of the data on
either side of the border.

I just inhabit a place where detailed mapping is always going to be
haphazard. Too many land, not enough people, not nearly enough
network connectivity.

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