The election Commission releases the voter registration data which includes name, address, birthdate, registration date, party affiliation, precinct/ward info. After each election they release data showing who voted (of course not for whom). They also release a Street Listing which contains the Occupation. The data for all of these is maintained by city workers on a statewide database.
As a result my data base all of this information including the voting history since 1997 (without the last month's of data so there are a few more, registration closed on the 14th).
59,237 registered voters
when people move away they remain registered for a while although if they
reregister somewhere else in the state that removes them from the Cambridge list.
43,847 voted in the 2008 election
12,995 voted in the 2007 municipal election
27,329 voted in the 2006 election
The overall count of registered voters has remained relatively constant (as has the population). The number of people voting in the local elections had decreased by huge amounts over time and 2007 was a low. It will be interesting to see if drops again which is expected.
The population changes rapidly. 16,587 people registered since the 2007 municipal election; 6,743 have Student as Occupation.