This metric is part of the Business and Human Rights Resource Centre's Tea Transparency Tracker project. 

Without supply chain transparency, workers don’t know where the tea they pick goes and remediation for abuses from forced labour to gender-based violence stop at the estate instead of going up the chain to where most of the value lies.  

The Business & Human Rights Resource Centre addressed this gap by approaching 65 companies with a request for them to disclose the estates and bought-leaf factories that they source their tea from, to be held centrally in the first Tea Transparency Tracker - hosted by WikiRate. We now have 3100+ estates and factories linked to 20 companies on the Tracker. 

A map of the tea supply chain and further information about the project can be found on the BHRRC's website.