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In a yaml config file created by OpenMapTiles I found the following syntax:

table: (SELECT geometry, class FROM layer_water(!bbox!, z(!scale_denominator!)))

The strings enclosed in exclamation marks obviously will be substituted by some provided values. My question is, how would this be done? I did not find anything about such a syntax for variable substition in yaml. Can someone please point me in the right direction? Or is this meant to be dealed with AFTER parsing yaml?

Regards Oliver

Oliver Bienert
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    Well it is definitely not part of YAML. However I cannot tell you which component takes care of replacing those substrings. Possibly the DB layer? – flyx Nov 07 '17 at 12:42

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I found it. The syntax is special to Mapnik and in my case to the PostGIS Plugin. The PostGIS plugin supports several special tokens. You can use them in subqueries and Mapnik will replace them at render time.

Oliver Bienert
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