[Talk-us] NHD Hydro Connectors

[David Fawcett]

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.
>
> --
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