Aunat is located some 60 km west by north-west of Perpignan and 25 km east by north-east of Ax-les-Thermes. Access to the commune is by the D20 road from Rodome in the west which passes through the village and continues east to Bessède-de-Sault. The D29 road comes from Fontanès-de-Sault in the south and passes through the length of the commune and the village before continuing north-west to join the D107 north-east of Belfort-sur-Rebenty. The commune is mostly rugged and forested but with farmland in the valley around the village.
The Ruisseau du Mouillou rises in the north-east of the commune and flows west gathering several tributaries from the north including the Ruisseau du Bernet and the Ruisseau de Valmajou before joining the Ruisseau de Romanis on the western border of the commune.
In 2010 the commune had 39 inhabitants. The evolution of the number of inhabitants is known from the population censuses conducted in the commune since 1793. From the 21st century, a census of communes with fewer than 10,000 inhabitants is held every five years, unlike larger towns that have a sample survey every year.[Note 1]
^At the beginning of the 21st century, the methods of identification have been modified by Law No. 2002-276 of 27 February 2002Archived 6 March 2016 at the Wayback Machine., the so-called "law of local democracy" and in particular Title V "census operations" allows, after a transitional period running from 2004 to 2008, the annual publication of the legal population of the different French administrative districts. For communes with a population greater than 10,000 inhabitants, a sample survey is conducted annually, the entire territory of these communes is taken into account at the end of the period of five years. The first "legal population" after 1999 under this new law came into force on 1 January 2009 and was based on the census of 2006.