[Talk-us] Low-quality NHD imports

Christoph Hormann osm at imagico.de
Fri Oct 13 17:34:16 UTC 2017

On Friday 13 October 2017, Kevin Kenny wrote:
> I remain unconvinced that importing or not importing has had any
> significant impact on whether people improve the map manually.

In case of NHD imports in the US there are certainly significant parts 
of the country where no NHD data has been imported and there is also no 
manual waterbody mapping worth mentioning - which would allow you to 
conclude there are likely also areas of NHD imports where at least so 
far this did not have a negative effect.  But in areas of significant 
interest, in particular popular outdoor destinations, i am pretty sure 
you can observe this - i showed an example from southern Montana where 
the limit of the detailed and accurate manual mapping clearly matches 
the limit of the previous NHD import or in other words:  The mapper 
mapping that clearly did not feel like bringing the NHD data to the 
same level of quality as the manually mapped area.  This is just one 
case and you cannot simple conclude it is the same everywhere else but 
i would not simply dismiss the idea that there is a discouraging effect 
of imports on manual mapping in some cases.

There are a number of possible measures that could be considered for 
improving old NHD imports:

* removal of unnecessary tags to reduce the baggage mappers would have 
to deal with when working on the data.
* removal of small unnamed streams which are not necessary for the 
overall river network connectivity in areas where the geometric 
accuracy is poor by current standards (and it is therefore usually 
easier for mappers to newly trace those streams instead of trying to 
improve the inaccurate data)
* creating maproulette challenges for fixing inaccurate waterway 
classifications - in particular waterways tagged 'waterway=stream' but 
with a name containing 'Creek' or 'River' will often qualify as 
waterway=river.  Same for artificial waterways with 'waterway=ditch' 
but names containing 'Canal' or ther other way round.
* creating maproulette challenges for unconnected waterways.
* adding missing 'intermittent=yes' to waterways in imports where this 
was not properly set based on the feature codes. 

Christoph Hormann

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