[Tagging] Using multipolygons to map bays in Alaska

Christoph Hormann osm at imagico.de
Sun Nov 18 12:22:30 UTC 2018

On Sunday 18 November 2018, Joseph Eisenberg wrote:
> Christoph, I was really looking forward to hearing how we can render
> good labels for bays and seas, based on a node and the coastline.
> Is there any possible solution the would work with Mapnik and
> CartoCSS?

Well - as said the principal obstacle here is that the coastline way 
data is not in the database.  Changing that would be relatively easy to 
do during a database reload.  OSM-Carto missed doing any adjustments 
with the last reload, the one that switched to Osmium for MP assembly, 
so some looking ahead would be necessaray for that.

But as also said for this kind of analytic application the raw coastline 
way data is not necessarily the most suitable or efficient solution.  
So the approach of preprocessing the coastline data and then putting 
that into the database is likely more suitable.  Many map styles 
already do that, in particular ones based on a vector tiles framework, 
using osmcoastline processed data (which OSM-Carto gets from the 

No matter what preprocessing you do and how you get the results into the 
database you still have to think about how to efficiently query the 
context of a bay/strait node to make the assessment you need.  We 
already had some discussion on this under one of the issues i linked to 
back in the days.  Of course this is related to preprocessing the data 
as well because you will want to put it in the database in a form that 
is efficient to query in the form you want to use.

Christoph Hormann

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