[Imports] Import of forests, farmland and other types of land cover for Sweden generated from Naturvårdsverkets Nationella Marktäckedata 2018

[Christoph Hormann]

On Wednesday 17 April 2019, Grigory Rechistov via Imports wrote:
>
> In the PDF on pages 52-55 there are English descriptions of classes
> used in the original raster: 
> https://wiki.openstreetmap.org/wiki/File:NMD_Produktbeskrivning_NMD20
>18Basskikt_v1_0.pdf . Note that we used not all of these classes, and
> in fact merged several classes of forests into a fewer sets of groups
> of OSM-tags.

That does not really help much - except for recognizing that the classes 
probably (based on the English description - which might be incomplete 
of course) do not match the tags in OSM in most cases, for example

* landuse=farmland is not the same as "arable land"
* landuse=grass is not the same as "vegetated other open land" - which 
is not limited to herbaceous vegetation and includes everything with 
>10% vegetation coverage (which frankly can also be lichen alone)
* landuse=forest is not for every area with more than 10% crown cover in 
trees >5m height (which can be almost anything - gardens, parks, 
orchards, scrub - as well as grassland and heath with scattered trees 
obviously).

Note these are just the "wishful thinking" specifications of course - 
the data does not actually have to represent them.  How they actually 
want to distinguish 10% tree cover >5m high from lower woody vegetation 
based on multispectral imagery along is doubtful.  Typically such 
classifications have error rates of at least 5-10 percent, often much 
higher.

> This import is meant to convert
> areas with *no data* into areas with *some data*. 

That is the standard "bad data is better than no data" argument.  With 
that we could have completely tiled the world with data from some 
global land cover classification project a long time ago.  Luckily for 
OSM we have refrained from doing that.

-- 
Christoph Hormann
http://www.imagico.de/