[Talk-GB] Mapping of Kielder Forest(s)

[Russ Garrett]

I've been doing some exploratory mapping around Kielder Forest which
involves making fairly substantial changes to what currently exists in
OSM, and I have received some changeset comments questioning this, so
I think it would be useful to get some consensus on what I'm doing
here.

## The current situation
A good example: https://www.openstreetmap.org/#map=14/55.1254/-2.4627

(Kielder Forest is composed of several smaller named forests, of which
Wark Forest is one, which is an additional complication which I'm not
going to go into at the moment.)

This large area of forest has been meticulously mapped as many
hundreds of small polygons, mostly tagged landuse=forest. The polygons
are split at narrow breaks in the trees as seen in either Bing imagery
or OS StreetView.

Some of these polygons (but by no means all) have the name of the
forest tagged on them.

## The problems with this approach
1) The use of name tags here is not ideal - it violates the "one
feature, one element" principle. From a rendering perspective this is
also bad: at higher zooms, there is an unavoidable mess of identical
name labels, and at low zooms a label is missing when it should
clearly be shown - these are big forests and well deserving of a label
at low zooms.

2) Tagging all these individual polygons as a multipolygon would
resolve this, however doing this with the existing forest polygons
will result in a very large multipolygon with hundreds of outer rings.
This is unwieldy to edit and, to some extent, also to render.

3) Kielder is a working commercial forest, with a significant area of
trees being felled and replanted on a yearly basis. There is no
guarantee that the forest will keep the same gaps after replanting,
and so constant tedious fiddling with the outline polygons will be
required to keep the map accurate.

There is, I think, a better way.

## Proposed solution
These landuse polygons should be merged into much larger polygons,
which encompass smaller breaks in the trees. These larger polygons can
then be combined into a multipolygon which represents the entire
forest.

There is an existing, well-supported tag for mapping these tree
breaks, although it doesn't see much use in the UK: man_made=cutline.
These cutlines mapped as ways are much easier to manipulate than
polygons when the planting changes. They are rendered by OSM Carto.

I appreciate that a lot of work has gone into mapping this area and it
is obviously a shame to have to revisit it all, but I think these
changes are important to allow the map to be easily maintained in
future, and to give these forests the rendering prominence they
deserve.

Comments are welcome, and I won't do any further mapping in this area
until people have had a week or so to comment.

Cheers,

-- 
Russ Garrett
russ at garrett.co.uk