migurski/TileStache — pull request #59 by thegreat (2012-05-16 00:12:33+00:00)
Title: Add a source layer identifier option to Mapnik grid provider 

Currently if you merge multiple UTFGrid layers into one file there's no nice way of distinguishing the merged data items.

This change adds an optional 'layer_id_key' parameter for mapnik grid provider which will add the source Mapnik layer name to each data item keyed by the provided value.