Reference: Maddieson 2013

Maddieson, Ian. 2013. Uvular Consonants. In Matthew S. Dryer and Martin Haspelmath (eds.), The World Atlas of Language Structures Online. Leipzig: Max Planck Institute for Evolutionary Anthropology.

https://wals.info/chapter/6

@incollection{maddieson2013wals6,
  address   = {Leipzig},
  author    = {Ian Maddieson},
  booktitle = {The World Atlas of Language Structures Online},
  editor    = {Matthew S. Dryer and Martin Haspelmath},
  publisher = {Max Planck Institute for Evolutionary Anthropology},
  title     = {Uvular Consonants},
  url       = {https://wals.info/chapter/6},
  year      = {2013}
}