This chapter addresses how to identify key categories1 in a national inventory. Methodological choice for
individual source and sink categories is important in managing overall inventory uncertainty. Generally,
inventory uncertainty is lower when emissions and removals are estimated using the most rigorous methods
provided for each category or subcategory in the sectoral volumes of these Guidelines. However, these methods
generally require more extensive resources for data collection, so it may not be feasible to use more rigorous
method for every category of emissions and removals. It is therefore good practice to identify those categories
that have the greatest contribution to overall inventory uncertainty in order to make the most efficient use of
available resources. By identifying these key categories in the national inventory, inventory compilers can
prioritise their efforts and improve their overall estimates. It is good practice for each country to identify its
national key categories in a systematic and objective manner as presented in this chapter. Consequently, it is
good practice to use results of key category analysis as a basis for methodological choice. Such a process will
lead to improved inventory quality, as well as greater confidence in the estimates that are developed.