[Tagging] Stop the large feature madness (was: Tag for a plateau or tableland?)

Christoph Hormann osm at imagico.de
Thu Apr 18 09:47:48 UTC 2019

On Thursday 18 April 2019, Kevin Kenny wrote:
> I doubt very much that you're saying what you intended here.
> It comes across as saying, for instance, that lakes too big to map on
> the ground in a single day should not be mapped, or should not be
> named. I think that making large waterbodies disappear would be
> ridiculous.

You apparently misunderstood what i said.  My 'surveyable in a single 
day by a single mapper' rule of thumb refers to mapping something as a 
single feature.  A river several thousand kilometers long for example.  
The river is locally still a verifiable element of the geography and 
can be mapped - piece by piece as it is generally established practice 
in OSM.  But if you create a feature for the whole river extending over 
thousands of kilometers that is not something you do based on local 
knowledge, that is based on social conventions you have read up in a 
book, on wikipedia or elsewhere.

As far as physical geography is concerned (so i leave out boundary and 
route relations here - which are a different thing) we have essentially 
only two types of feature that are generally accepted to be mapped with 
large relations:  lakes and islands.  Both of these were not always 
mapped this way - large lakes were for a long time mapped only 
locally - like the coastline.  Both of these are technically 
unnecessary to be mapped this way (there is no actual information 
transported in assembling the ways into an MP relation) because their 
geometry derives non-ambiguously from the locally mapped water 
outlines.  The decision to create MPs none the less mostly comes from 
the desire to have consistency with smaller features (which are 
obviously locally verifiable as a whole).

Everything else in physical geography is typically mapped locally piece 
by piece like the rivers and creating large features - while done by 
some mappers for the purpose of label painting - is generally disliked 
by most mappers because it is very hard to work with these and 
represents no additional meaningful information.

> Moreover, if you've mapped something on the ground, what difference
> does it make how long it took?

It is a rule of thumb.  The rule itself has no meaning on its own, it is 
designed to make it easy to determine a reasonable limit.

> I understand that there are fairly severe technological issues at
> present, where a plethora of enormous multipolygons breaks some of
> the software tools.

My argument is not a technological one, it is a social one.  Mapping 
only things verifiable based on local knowledge in OSM is essential for 
the social cohesion of the project across many different cultures world 
wide without creating an imperialistic dominance of some cultures over 

Christoph Hormann

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