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On 09/02/2011 20:27, Kevin Peat wrote:
<blockquote
cite="mid:AANLkTi=-JvfxqXYKGVT=Hg4Z9b0dUGkKO3AVGt_MO85Z@mail.gmail.com"
type="cite">Hi Jason,<br>
<br>
I am the mapper (user:devonshire) who imported the woods in your
first example around Dartmouth but it was last May so not exactly
recently. The woods that are there now are a lot better than the
NPE traced ones that we had before. I took the view at the time
that importing the VectorMap data would be a major improvement.<br>
<br>
Since the Bing imagery (old as it is) became available I am not
sure why anyone would bother importing VectorMap woods as it is a
lot less hassle to trace from Bing and just take the names from
the OS StreetView. Ultimately I will probably replace the OS
sourced data but it isn't a big priority for me right now. Feel
free if you have nothing better to do.<br>
<br>
The VectorMap data for streams is good especially as they are
virtually impossible to survey well on the ground. Filling in the
blanks may seem like a good idea but whether it is a track
bridging the stream, the stream is piped or just disappears for a
bit (as often happens in wetland areas) is hard to know without a
survey.<br>
<br>
Kevin<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<div class="gmail_quote">On 9 February 2011 18:42, Jason
Cunningham <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:jamicuosm@googlemail.com">jamicuosm@googlemail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt
0.8ex; border-left: 1px solid rgb(204, 204, 204);
padding-left: 1ex;">OS VectorMap District is an excellent
source of data for features like streams and woodland, but
these layers of data tend to be a bit of a mess and need to be
stitched together as part of a method in importing into OSM.<br>
eg Streams will end when they meet a bridge, then reappear the
other side of the bridge, so for OSM you need to link all the
separate sections of the streams into one long stream<br>
<br>
Started to notice that the VectroMap District data in its
"raw" state has started to appear in the map, from more than
one mapper<br>
<a moz-do-not-send="true" href="http://osm.org/go/erduA_U9K--"
target="_blank">http://osm.org/go/erduA_U9K--</a><br>
<a moz-do-not-send="true" href="http://osm.org/go/eugeBnUca-"
target="_blank">http://osm.org/go/eugeBnUca-</a><br>
You can see stream are broken presumably at locations of
bridges, and woodland has strips missing presumably along
paths (and is also made up of several sections if you look at
it in an editor)<br>
<br>
Doesn't appear to be guidance in the wiki about how to deal
with VectorMap District. I just want to check I'm right in
thinking this is the wrong way to go about it? If so I'll try
and write up some guidance in the wiki.<br>
<font color="#888888">
<br>
Jason<br>
<br>
</font><br>
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</blockquote>
</div>
<br>
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</blockquote>
Jason has pointed out a number of issues with the natural features
layer of VectorMap District. I'd like to add a few more:<br>
<ul>
<li>Larger Streams & Rivers are only present as areas, not
vectors, as well as not being connected. Absence of vector
waterway data, particularly when not connected, means that OSM
data is useless for any kind of hydrographic or hydrological
analysis. Old traced streams from NPE maps on the other hand are
still fit for this purpose. Use case: low cost simulation of
environmental issues (water pollution, flooding) for charities,
campaign groups etc.</li>
<li>Woodland parcels can be incredibly minute and over detailed:
to an extent that the detail cannot be verified on the ground.</li>
<li>Woodland parcels are often not woodland. So far I have found
parkland with interspersed trees (see any golf course), small
groups of trees with no corresponding ground layer (not a wood,
see first example posted by Jason), <a
href="http://www.flickr.com/photos/sk53_osm/4611517582">wetland
features</a> (exuberant over-interpretation of aerial images),
avenues of trees, suburban and urban parks where one or two old
specimen trees have large spreads, scrub...</li>
<li>Woodland parcels are often separated by a short distance to
provide for a path, even when the canopy is closed. <br>
</li>
<li>Many areas are artificially divided by lines corresponding to
the 1 kilometer lines of the National Grid.</li>
</ul>
The main problem is that although VDM shapes are often extremely
detailed, in many cases the accuracy and detail is spurious. <br>
<br>
Another problem is that adding areas of streams or many woodland
fragments places a significant burden on a) servers; b) editors and
c) consumers (see Frederik's post). I like having these things on
the map, but I do want to be able to have maps on the Garmin which
cover a useful area. Thus adding this kind of detail may mean
thinking either about adding new tags or extending existing tagging
in the way which is happening with buildings. Personally, I might
start trying to use natural=tree on areas and ways so that some of
these 'woodland' categories can be separated out: an obvious render
approach is like that used by the OSGB for 'scattered trees'. <br>
<br>
Note that there are vector waterways and woodland available in the
OS OpenData set which might be more useful as a starting baseline
for later refinement, notably Meridian 2.<br>
<br>
I've recently been looking at Coed y Brenin, in N Wales, one of the
Forestry Commissions larger forests. I've added from Bing two areas,
but had contemplated using VDM to do the rest because its so big,
and reasonable involved. At the moment although MTB trails are well
mapped none of the forest they traverse is there, so mapnik looks
peculiar. However, VDM for this area creates around 4000 polygons of
woodland: some of them tiny. I doubt if anyone will ever be in a
position to verify each of them, so I dont see that it makes
particular sense to import this data, but on the other hand I have
no desire to spend days tracing a 40000 acre forest!<br>
<br>
Jerry<br>
<br>
<br>
<br>
<br>
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