[OSM-talk] OpenStreetMap Carto database schema change

[Christoph Hormann]

On Tuesday 31 January 2017, Dave F wrote:
> What benefits does this bring to the end user zooming & panning
> around? You've produced a demo so I presume there is one.

I think there is currently no comprehensive list of practical direct 
effects this has.

The most significant ones are likely various differences in the way 
polygons are interpreted and rendered.   

Of these differences the most prominent one is probably due to loading 
each multipolygon relation as a single feature into the rendering 
database (osm2pgsql -G option) rather than splitting it into separate 
components.  This makes a strong difference w.r.t. rendering of labels 
for administrative boundaries.  However this is not mainly what we are 
asking for feedback here since this is a change which is already well 
known and well tested in its effects.  We are also aware that this 
change will likely require tuning the style in terms of label placement 
in the long term - which is however not a point of concern right now.

Where feedback is most useful are the more suptle changes which will 
only have a visible effect in a smaller number of situations.  See the 
PR Paul linked to for details.  In particular it would be important to 
know if there are situations where the new database schema leads to 
incorrect mapper feedback through the the way things are rendered.

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