CLEAN: Annan expects Syria truce by April 12 as fighting rages

The transcript discusses the Syrian government's withdrawal from populated centers, the halt of military movements into cities, and a 48-hour period for the cessation of violence by all parties, including the Syrian opposition. It also mentions Mr. Anna's planned visit to Tehran on the 11th.

What does the term 'populated centers' refer to in the context of military withdrawal?

What is the context of Mr. Anna's visit to Tehran?