When Augustus conducted a census it was to determine the number of Roman citizens, as noted in the Res Gestae Divi Augustus.
http://classics.mit.edu/Augustus/deeds.html
http://classics.mit.edu/Augustus/deeds.html
Quote:8. When I was consul the fifth time (29 B.C.E.), I increased the number of patricians by order of the people and senate. I read the roll of the senate three times, and in my sixth consulate (28 B.C.E.) I made a census of the people with Marcus Agrippa as my colleague. I conducted a lustrum, after a forty-one year gap, in which lustrum were counted 4,063,000 heads of Roman citizens. Then again, with consular imperium I conducted a lustrum alone when Gaius Censorinus and Gaius Asinius were consuls (8 B.C.E.), in which lustrum were counted 4,233,000 heads of Roman citizens. And the third time, with consular imperium, I conducted a lustrum with my son Tiberius Caesar as colleague, when Sextus Pompeius and Sextus Appuleius were consuls (14 A.C.E.), in which lustrum were counted 4,937,000 of the heads of Roman citizens. By new laws passed with my sponsorship, I restored many traditions of the ancestors, which were falling into disuse in our age, and myself I handed on precedents of many things to be imitated in later generations.
