[OSM-newbies] newbies Digest, Vol 37, Issue 32

[Phil Monger]

The field boundaries on 25k maps are a derivative layer based on the larger
scale surveys - they come from data from as recently as 2009 and not older
than 2002. The problem is, if they change (and are not reported) and such a
change is not visible from an aerial survey, the lines won't move. They're
inaccurate rather than just old. This happens very easily when a hedge or
fence is removed but a ditch (or even just a grass row) creates what looks
like the same boundary on the map. Strictly speaking, a line on a 25k map is
a "linear topographical feature" and they implicitly state on the bottom
that they should not be seen as field boundaries. Field surveys went out a
long time ago. (they used to all be numbered, with their exact acreage
recorded).

Having said that, it all depends on where you are. When I led a geological
project in the Mendips we found that the field boundary lines were
completely invaluable - only a couple were out and it was clear why - wire
fences! Nearly all were exactly right.

The issue of footpaths on OS maps is about as contentious as they come. Soon
as anyone marks one on (council supplied data, included) a land owner
protests it. Arguing that although the land is 'access granted' they have
the right not to have their land advertised as a recreational site, and it
goes on ...
Even some of the National Trails aren't marked as there are access disputes.

The green lines on OS maps are therefore typically only marked where the
walkway is a clear physical path between two sections of land. Infrequently
do they cross land (even though in many cases they do, with rights to do
such.) Anything else is given the ambiguous dotted line and the title
"track."

Again Dave, cause and effect are two different things. Just because a
council choose to give the OS their data does not mean they *have to* - they
could just as well say "f*** you" and give the data to OSM.

Unfortunately councils are just ill-informed. Surely, if nothing else, OSM
is here to spread it's message and it's ethos? Why not ask your council for
the data once it's done? Or would that be creating a subsidised fork of OSM?
Would we notice? Would anyone care? It's a ludicrous position.

On 24 March 2010 23:06, Dave F. <davefox at madasafish.com> wrote:

> Phil Monger wrote:
> > Finally, *no* OS data currently in use exists from a survey prior to 1999
>
> I'm not sure of an exact age but the field boundaries shown on 1:25k
> maps are well over 11 years old. They are hideously out of date.
>
> My local council is paying a surveying team to walk all the paths in
> their jurisdiction to create a definitive map which they will then pass
> on to the OS *at no charge*. The OS therefore *do* receive subsidisation
> from the taxpayer.
>
> Dave F.
>
>
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