Source: https://pokemongo.gamepress.gg/guide-using-incense
Incense pulls from the biome you are in when the spawn occurs. The Incense spawns will resemble what usually spawns in the area… similar amount of weather boosting, similar frequency of 2nd and 3rd evolutions, and similar species. Note that this does not mean Incense will give the same Pokémon you get from a specific nest. Incense only pulls from biome and ignores nest information. If Incense is used in a remote area with no defined biome, a wide variety of random Pokémon can spawn.
TL;DR
It will attract pokemons that are naturally going to spawn in the area. If there are no "natural" pokemons, random pokemons are attracted