Even Rouault wrote:

> Perhaps you could play with the SIMPLIFICATION and SIMPLIFICATION_MAX_ZOOM 
> options ?
Sure, as I wrote I admit that my test did not make much sense, but trying 
things before reading the manual sometimes reveals something interesting.  

> Perhaps you should also use an already simplified layer for the lowest zoom 
> level (see the CONF option)
For sure yes, coordinate space of 4096x4096 is far too small for this dataset.

> Are you sure you get polygons with less than 4 points ? Normally they should 
> be discarded.
Quite sure yes by looking at what the ST_IsValidReason from the SQLite dialect 
ST_IsValidReason(geometry) (String) = Invalid: Toxic Geometry ... too few points

There are other variants of invalid geometries and actually a few valid as 
well. Here is one example with an invalid component

  MULTIPOLYGON (((516384 6815744,516384 6815744,532768 6815744,516384 6815744)),
((516384 6815744,516384 6815744)),((516384 6815744,516384 6815744)))

My zero tile is here http://www.latuviitta.org/downloads/0.pbf

-Jukka Rahkonen-
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