[Talk-us] What to do with unnamed NHD streams

Michal Migurski mike at teczno.com
Mon Oct 29 03:58:21 GMT 2012

On Oct 28, 2012, at 8:51 PM, Paul Norman wrote:

> Background: I'm working on converting NHD to .osm format
> 2. Some ways are very over-noded. The NHD accuracy standard is <12m error
> 90% of the time. Running a 1m simplify in JOSM reduces the number of nodes
> to 25%-50% of what it was before. Like everything with the NHD, this varies
> from region to region. I'm thinking a 2.5m simplification would be best -
> it's 1/5th of the accuracy standard. Of course, running a simplification on
> a dataset this large is a challenge in itself.

Does it all come in shapefile form? The simplification would be a relatively easy (though time-consuming) task for PostGIS on a server with sufficient storage, outputting new shapefiles for ogr2osm. I can help with this using one of our office servers that we use for such tasks.

> 3. A lot of NHD is very minor streams "only of use to hydrologists." There
> are streams that you would be hard pressed to locate if you were there in
> person and in some cases they do not exist anymore.
> A sensible solution in any NHD translation may be to drop any FCode 46003
> (intermittent) streams without a name. It may also be worth dropping FCode
> 46006 (perennial) streams without a name.

Can these be simplified to a lower level of accuracy?


michal migurski- mike at stamen.com

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