The Aztec and Inca civilizations were different from each other in terms of public work projects, because the first one focused on agricultural innovations, while the second one focused on road constructions.
Aztec Civilization: On one hand Aztec people adopted an agricultural system of farming which was called "Chinampas". This system was highly important for them because it helped them to transform in a short period of time, their land into a fertile and productive island.
As it's known, Aztecs built their capital city "Tenochtitlan" on a marshy island with limited resources, which made life for them quite difficult. That's why they worked hard and looked for a convenient way to keep their city on a swampy land.
Inca Civilization: On the other hand, Incas focused on building a strong road system. In order to make it happened, they implemented a labor tax known as "Mitaa". With Mitaa, people were requested to provide labor for certain periods of the year, in order to build a road, which reached 10.000 miles long.
The road system was important for Incas because it was used for many purposes. One of them was being as the main route of transportation for "Chasquis", who were runners in charge of carrying messages from one end of the empire to another. Besides that, the Incas roads network was used for the military troops too. Due to the road system, the army could bring control to remote trouble areas of the empire easily. Apart from this, Incas also built guests houses along the roads, in order to provide shelter for travelers.