National, regional and local governments around the world are taking steps to tackle climate change. In order to do so they need to track and report their climate data. However, in some instances, greenhouse gas (GHG) emissions are hard to accurately track and/or quantify.
Notation keys are used in greenhouse gas (GHG) emissions inventories where data is absent or incomplete, to indicate why data is lacking. The use of notation keys is an internationally recognized good practice. In fact, a GHG inventory that lacks proper representation of all emissions, either through quantification or the use of notation keys, does not comply with the completeness principle.