[Talk-us] A Friendly Guide to 'Bots and Imports

[James U]

On Thursday, August 05, 2010 06:32:04 pm you wrote:
> On Thu, Aug 5, 2010 at 6:10 PM, James U <jumbanho at gmail.com> 
wrote:
> > I have to say that after importing a large amount of NHD data (most 
of NC
> > and MN) that it is of varying quality, as was the preexisting water
> > related data already on the server.  In general, I agree with Ian that
> > it is higher quality (both resolution and accuracy) than the 
preexisting
> > data that largely consisted of quickly drawn Yahoo traces.  I saw very
> > little evidence of on the ground surveying of these features and 
don't
> > think the import will hinder most people from participating in OSM writ
> > large.
> 
> On the other hand, my (extremely limited) experience is that the
> aerial water traces for Disney World were superior to the NHD import
> (so I quickly deleted all the dupes from NHD). But the swamps were a
> lot more useful, since you can't really tell if something's swampy
> without physically going there. I love how all these "islands"
> suddenly made sense:
> 
http://www.openstreetmap.org/?lat=28.29&lon=-81.5191&zoom=14&layers=M

You are certainly correct that there are many examples of other imported 
waterbodies and streams that _are_ better than NHD, this is why I 
strongly recommend that importers of the data do a careful scan of the 
data and when there are duplicate features to try to use a high quality 
aerial photo to make a judgment of which is the better data.  For some 
features, such as multipolygon lakes with islands, I have mixed and 
matched different parts of the NHD and the previously uploaded feature 
(sometimes you can tell where mappers got tired of tracing).

In some cases, for example in dams where water levels fluctuate and 
aerial photos might represent a low water phase, the NHD may have 
better data that are representative of the level that the reservoir is 
maintained at.