[Tagging] Feature Proposal - Voting - Rivers Classification

[Christoph Hormann]

On Tuesday 17 October 2017, Kevin Kenny wrote:
> It's impossible to base a rendering decision on something that isn't
> represented by any tag.

That is not true, you can produce a lot of information through analysis 
of the data and by connecting it to data outside of OSM (which is 
usually outside of OSM because it is outside the scope of OSM).

Most obvious example is label placement.  If and where there is space to 
place a label for a certain feature is not represented by a tag.  
According to you it would therefore be impossible to render labels 
without overlap.  But renderers do this by analyzing the data and 
selecting label positions based on that.

Or the fact that highway=traffic_signals does not usually have a 
direction tag because if you want directed rendering of traffic signals 
in a map you can determine the direction by analyzing the data and 
determining the direction of the intersecting roads.

The OSM database is not a rendering database, it does not try to contain 
everything you need to render a map in the form that is most convenient 
for rendering.  It is a generic geo-database for information about the 
world that can be verifiably observed on the ground and that is useful 
for map rendering or other applications.

> 'Tagging for the renderer' is telling a lie
> to make something look good, not entering a fact into the
> database so that some rendering can make use of it.

If you newly introduce a tag that can never be 'Tagging for the 
renderer' in that sense because use of a newly introduced tag is never 
wrong in the sense it contradicts established use.  I recently coined 
the term 'Preemptive tagging for the renderer' 
(http://blog.imagico.de/social-engineering-in-openstreetmap/) for this 
kind of tag which is being created because the inventor considers it 
useful for map rendering although it is either not verifiable or it is 
not a good way to represent a verifiable observation (like the famous 
is_in).

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