Annan District is located at the southwestern tip of Tainan City. It borders the Taiwan Strait to the west and Anping District, West Central District and East District to the south across the Yanshui River. It is adjacent to Cigu District and Sigang District to the north. And it is next to Yongkang District and Anding District to the east.

The Precinct covers a square area of 107.2 km²,which is divided up into 51 villages and 856 neighborhoods. Currently there are a total of 69,973 households with a population of 199,118. To the east and north, the Precinct is next to Yongkang and Shanhua Precincts by the Yanshui River. To the south, it is next to Fourth and Fifth Precincts where the Yanshui River and Jianan Irrigation Canal are merged and exit to the ocean. To the north, there is Zengwen River that passes through the district as it makes its exit into the ocean. The coastline is 14km long with its southwest facing the Taiwan Strait.

There are mostly farmlands, lands for industrial use and fisheries within the Precinct. The residents mostly rely on farming and trading. Its people live a simple life and are close with one another in a supportive and genuine way. There are three industrial parks in the region: Zong Tou Liao, He Shun and Tainan Technology.