On Tue, Apr 26, 2011 at 7:49 AM, Ben Supnik <[email protected]> wrote:
> Hi Y'all, > > The USGS was kind enough to send me the latest shapefile extract for the > NHD yesterday. So my question is: is there some way I can process and > repost this data that would make it more suitable for importers? > There already is a process on the NHD wiki page. > > I read the wiki pages on NHD imports a few weeks ago, but found the USGS > download process to be difficult - there wasn't a simple "click here and get > the shapefile you need to feed into shp2osm" type interface. > The process is to download a subbasin, convert to OSM, and import (checking for existing waterways). > > I could rehost the NHD files on my company's servers for a while, perhaps > even in .osm format. > > But...the data extract is 'the whole database' split only by layer and file > size. For example, the water body layer (which contains area lakes and > ponds) comes as 5 shapefiles of between 500 and 800 MB each; there isn't any > spatial partitioning, so you would need to load the entire data set to pull > out lakes of interest for a given bounding box. > Converting these into OSM probably won't be very helpful at this point. > > I could break the data up in a few ways... > - It looks like the reach codes contain sub basin IDs as their first 8 > digits. > - I could break the data into square tiles. > - I suppose it could be split by state. > - 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) - Square tiles won't line up with existing NHD imports - States wouldn't line up either but may be easier to merge. > > For the second two cases, the data is not naturally split along those > boundaries, so I'd have to either induce a cut (not preferable) or have a > few features be not quite where they'd be expected. > > Anyway, I'm open to ideas...my end goal is to do enough of the GIS > processing type work that mappers who are enthusiastic and want to improve > their local water areas (but aren't comfortable with command line tools and > shapefiles) can grab a pre-converted chunk of data, inspect it, and import > some of it. > > (Side note: I tried to do a test of a importing a multipolygon as a vector > background in Potlatch 2, and it failed for both .osm and .shp format data, > https://trac.openstreetmap.org/ticket/3701 - has anyone successfully > imported water data this way, or should I expect that users will have to use > JOSM?) > Yes, I wrote my shp-to-osm Java code specifically to handle the multipolygons in NHD and it seems to work fine. I even uploaded some of them in Wisconsin. I stopped because the server was periodically rejecting my imports and would leave thousands of orphaned nodes. This is when I stopped importing NHD. > > cheers > Ben > > PS If anyone wants the raw data, let me know...I have enough broadband that > I could push it to a handful of users if interested. > We have NHD from circa last year on the OSMF US servers. It may be useful to update that data. I'll be in contact when we have the space in a week or so. -Ian
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