[Talk-us] NHD Hydro Connectors

[Paul Norman]

Here in Canada with the NHN import the portion of streams through lakes and
wider rivers were imported with sub_sea=stream sub_sea:type=inferred
oneway=yes accuracy:meters=-1 (and source/attribution tags), but that import
needed a lot of clean up after it. I've been changing the sub_sea=stream to
waterway=stream|river as I go through my area doing cleanup.

My recollection is that a few months ago you couldn't see the streams under
natural=water areas but after a style change you could.

-----Original Message-----
From: David Fawcett [mailto:david.fawcett at gmail.com] 
Sent: Friday, February 18, 2011 8:59 AM
To: Phil! Gold
Cc: talk-us at openstreetmap.org
Subject: Re: [Talk-us] NHD Hydro Connectors

Thanks for your input Phil.  I don't have strong opinions about what data
should be stored, I just think that when the default public map looks
ugly/broken, people start to question other data elements as well.

It will be interesting to see if people can actually build and maintain
hydro networks based on the imported NHD data.  I would think that for the
purpose of building networks, one might always want to work with the
original data.

As an aside, if one is trying to build a network, it is useful to know that
in the Great Lakes, some shorelines are included in the streamlines data.
The shoreline-based streamlines for islands can definitely throw an error in
network creation because their start node and end nodes are the same.

We also have to remember that the NHD is a 'living' data set.  There is
significant editing going on in two major watersheds (HUC8s) in my area.

David.

On Fri, Feb 18, 2011 at 10:36 AM, Phil! Gold <phil_g at pobox.com> wrote:
> * David Fawcett <david.fawcett at gmail.com> [2011-02-18 10:13 -0600]:
>> In some areas where the National Hydrography Dataset (NHD) has been 
>> imported, the rendering of the data is less than desirable.  I am not 
>> sure if this is something that should be fixed in renderers or in the 
>> data.
>
> IMHO, it's a rendering issue.  First off, it also affects the current 
> best practice (as I understand it) of mapping wider waterways as 
> riverbank plus linear way; if the linear way is tagged 
> waterway=stream, you get the same artifacts.
>
> Secondly, it is often the case that waterways are considered to 
> continue through bodies of water, which would indicate the necessity 
> of the connecting linear ways to accurately reflect local naming of 
> water features.  I know of several places in my area where a river was 
> dammed to form a lake, the lake is known as "Such-and-such Reservoir", 
> but the original river is still considered to be running through the 
> middle of the reservoir and shows a such on maps.
>
> Thirdly, having a complete waterway network is a potentially useful 
> thing (for many of the reasons the NHD adds the connecting ways in the 
> first
> place) so their presence shouldn't be discouraged.
>
> My conclusion is just that the renderers need to handle linear streams 
> on top of water areas (natural=water or waterway=riverbank) better and 
> no tagging changes should be needed.  Submitting a patch for this is 
> on my list of things I plan to look at eventually if no one beats me 
> to it, but that's a long list with other things ahead of stream rendering.
>
> --
> ...computer contrarian of the first order... / 
> http://aperiodic.net/phil/
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