Not a historian, but I lived and studied in Peru, and have studied Andean History to an extant. I've never heard of any Incan maps in existence. Hopefully a trained historian can shed more light on the matter, but in the meantime here is what I have learned.

The Incans didn't have a writing system per se, but they did have Quipu

Quipu consisted of a horizontal string, and beneath it were verticle strings upon which were tied various knots. Quipu was used for census, and keeping track of numbers. Trained runners called chasqui were used to transport messages between cities, either oral, or with said Quipu.

Nobody now knows exactly how Quipu was written anymore, but theories include the number and placement of knots as differentiating different figures, as well as the location of the strings.

Said Quipu aided the Inca in creating a very centralized empire without a strict writing system.

Source: http://www.ancientscripts.com/quipu.html as well as Comentarios Reales de los Inca by Garcilaso de la Vega. My source is in Spanish as I am bilingual, but there are various english translations which are available online (Search for Royal commentaries of the Incas). However, while Garcilaso is a fascinating charactor, do keep in mind that he had a number of biases in his writing, and that he mainly wrote in Spain, long after he had left Peru. http://shemer.mslib.huji.ac.il/lib/W/ebooks/001531300.pdf