Armissan is part of the urban area of Narbonne and is located just 2 km east of the city immediately south of Vinassan and inside the Regional Natural Park of Narbonne. Access to the commune is by road D68 from Narbonne passing through the town and continuing south-east to join the D168 to Narbonne-Plage at the southern border of the commune. The D168 from Narbonne to Narbonne-Plage also passes through the south of the commune. There is also the D31 going south from Vinasson through the west of the commune to join the D32. The A9 autoroute passes through the west of the commune but has no exit - the nearest exit is Exit 37 at Narbonne. The commune has large forests in teh south-west and in the north with the rest of the commune farmland.
The Ruisseau Mayral with many tributaries flows through the village west to join a network of canals west of the A9.
In 2009 the commune had 1,547 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 2002, 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 in 1 January 2009 and was based on the census of 2006.