[Talk-us] NHD data extract

[James Umbanhowar]

On Tuesday 26 April 2011 09:35:00 Ian Dees wrote:
> On Tue, Apr 26, 2011 at 8:30 AM, Ben Supnik <bsupnik at xsquawkbox.net> wrote:
> > Hi Ian,
> > 
> > Where on the OSM servers is the current NHD data, and in what format?  I
> > didn't see it referenced in the wiki work-flow.
> 
> They're currently only used to render TopOSM and aren't available via HTTP
> or whatnot. I had plans to convert it all to OSM but ran into the problem
> 
> you're seeing below:
> >  - Not all of the data types contain enough information to split like
> >  
> >> this (last I checked the linear features were the only ones with reach
> >> code. Polygonal features don't contain subbasin information)
> > 
> > I am looking at this now.  Some of the polygonal lakes definitely do
> > contain reach codes, others contain NULL.  From what I can tell, there
> > are fcodes that indicate that there is no reach code (or any meta data).
> > 
> > For the polygonal "area" data (which includes large rivers) there are
> > indeed no reach codes. :-(
> 
> If I remember correctly the area data has some sort of ID which links it to
> the waterway (which has a reach code). The area data is what wraps a
> waterway when it has a width greater than some standard "too wide for a
> single line" width.

Some of the areas, namely large river areas, cross subbasin boundaries so this 
might be why they cannot be localized to one subbasin.  This would be an issue 
if there were to be one file per subbasin.  Either the entire riverbank would 
need to be assigned to one subbasin or it would need to be split at the 
subbasin boundaries.

This might also be the case for waterbodies.  I recall when I imported the 
coastal NC data there were many wetlands that crossed subbasin boundaries and 
were duplicated.