[Talk-us] Low-quality NHD imports
daveswarthout at gmail.com
Fri Oct 13 10:08:54 UTC 2017
Sometimes I think it might have been better if OSM had never imported Tiger
data. It is simply pitiful, almost worse than nothing, in many areas of
Alaska. Same with the coastlines and NHD water bodies. I know they
represent a first approximation and without any coastlines we couldn't have
a map, period, but the sheer amount of editing required to clean up the
horrendous data in Alaska is daunting indeed. Same for the riverbanks. I
usually delete them and start over fresh because it's easier to create new
ones than to try to adjust and align the bad stuff already in place.
Given the actual total length of coastline in Alaska, I would venture to
say it will never be cleaned up. Here is an example of a relation
(id:2057975) "glacier" imported from NHD that is actually many named
glaciers all rolled into one. I have been working hard for the past year to
add individual named glaciers in Alaska but I swear, looking at something
like this monster containing 542 members makes me think I'll never get it
Also, if you want to see something else that is really horrendous, take a
look at the Canvec imports for Canada; rivers and streams composed of many
tiny sections, water and woods where there isn't any. Sheesh!
Sorry, couldn't resist.
On Fri, Oct 13, 2017 at 2:18 PM, Wolfgang Zenker <wolfgang at lyxys.ka.sub.org>
> * Frederik Ramm <frederik at remote.org> [171013 08:06]:
> > there's a LOT of NHD:* (and nhd:*) tags on OSM objects, see
> > https://taginfo.openstreetmap.org/search?q=NHD%3A
> > - 1.9 million NHD:FCode, but also 188k "NHD:Permanent_" (note the
> > underscore), 10k "NHD:WBAreaComI", or 1.5m "NHD:Resolution" just to grab
> > a few.
> > I haven't researched who added them and when, but they would certainly
> > not clear the quality standards we have for imports today. Most of this
> > information can be properly modelled in usual OSM tags, and where it
> > cannot, it probably shouldn't be in OSM in the first place.
> > Is there any systematic (or even sporadic) effort of cleaning up these
> > old imports? Is there reason to believe that the neglect extends to more
> > than just the tags - do geometry and topology usually work well on
> > these, or are the funny tags a huge "this whole area hasn't had any love
> > in a long time" sign?
> the NHD imports that I have encountered so far have numerous problems:
> The data is several decades old, the so-called "medium resolution" is
> pretty bad, and the data was basically just dumped into the OSM database
> without any conflation happening. And larger rivers where often imported
> as monstrous riverbank polygons without the river itself as a flowline.
> The worst junk like lakes covering motorways has been mostly cleaned up
> by now, but it is still easy to see where NHD data has been imported by
> looking a KeepRights display of broken highway/waterway crossings.
> I clean up the imports in areas where I'm doing TIGER reviews, but I
> have to admit that a few times I have decided to work on different areas
> instead because the huge riverbank polygons where almost impossible to
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Chiang Mai, Thailand
Travel Blog at http://dswarthout.blogspot.com
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