[Talk-GB] OS and OSM

[Chris Hill]

On 11/03/11 10:19, Steve Chilton wrote:
> I have been asked by editor of the Cartographic Journal to write a short piece on the effect of the release of OS OpenData on the OpenStreetMap project, and I am just trying to gather my thoughts, and make sure I cover all bases.
> I was present at Blackadder's Society of Cartographers talk on "Why OSM won't be bulk importing OS OpenData" and am aware of the work Chris Hill has done on admin boundaries etc.
> Obviously also aware of the ITO work with OS Locator and what people have done with that.
> There was work on importing detailed water features, was that Chris as well (goes off to read back through his blog).
> Can anyone point me to others who have explored the possibilities that OS OpenData provided - PARTICULARLY if they can evidence WHY it is NOT of value to OSM?
OS Opendata gives us access to places we can't otherwise go, such as 
docks, but so does aerial photography. It provides features such as 
power lines and some water ways that cross land that we don't have 
access to.  It gives us access to the official, up-to-date boundary data 
that is just not available in any other form that we can use. It is much 
more up-to-date than some of the aerials and some of the various forms 
of data have names on them (Streetview and Locator) though that does 
have some small level of errors. There is also the postcode dataset 
which is a valuable source of data that would be very difficult to 
gather exhaustively otherwise.

On the down side the level of detail is low. The building outlines, 
especially houses, are clearly crude and only indicative. I have been 
adding buildings and, combined with a survey, addresses and it is useful 
to use OS Streetview where the aerials are too old to see recent 
developments or occasionally where buildings are hidden by tree cover, 
but generally Streetview is not as good as aerials, which themselves are 
not that detailed in some areas I'm interested in. The VectorMap is 
(counter to its title) really taken from a render layer. Waterways have 
annoying gaps where anything crosses them. Woods have somewhat chunky 
outlines and annoying gaps. StreetView has hints of tracks where the 
names remain but the track detail has been removed.

The alignment of Streetview (against multiple GPS traces) is 
consistently off in the areas I've used, but that could be the way 
someone in OSM has used it. Aerials are also off, but not as 
consistently, which means always checking the alignment before use.

Some of the datasets are more useful than others. BoundaryLine is very 
useful, VectorMap District Settlements by area seem to me to be total 
rubbish - horribly crude, undefined as to what they show and badly 
out-of-date.

I think OS Opendata has been useful, but it has also attracted the 
armchair tracer. Much of North and North East  Lincolnshire is only in 
OSM because it has been traced from OS OpenData. All of the detail from 
a ground survey is missing, yet the map looks quite complete at first 
glance. According to Jerry's blog ( 
http://sk53-osm.blogspot.com/2011/02/updating-pub-density.html ) Grimsby 
has no pubs, this because Grimsby has been traced not surveyed. OS 
OpenData made this possible but it is not directly responsible.

-- 
Cheers, Chris
user: chillly