After years of demanding greater political autonomy, residents were given the right to directly elect a Head of Government and the representatives of the unicameral Legislative Assembly by popular vote in 1997. Ever since, the left-wing Party of the Democratic Revolution (PRD) has controlled both of them. In recent years, the local government has passed a wave of liberal policies, such as abortion on request, a limited form of euthanasia, no-fault divorce, and same-sex marriage. On January 29, 2016, it ceased to be called the Federal District (Spanish: Distrito Federal or D.F.) and is now in transition to become the country's 32nd federal entity, giving it a level of autonomy comparable to that of a state. Because of a clause in the Mexican Constitution, however, as the seat of the powers of the Union, it can never become a state, lest the capital of the country be relocated elsewhere.

Answer this question, if possible (if impossible, reply "unanswerable"): When did people become able to vote for representation?
1997