Learn Spanish (Latin America): El censo analiza a más de mil ciudadanos. - The census analyzes more than a thousand citizens.

When making a comparison involving a specific number or amount like mil (a thousand), Spanish uses más de (more than) and menos de (less than). You use más que when comparing two different things or actions.

Why is there an a before más de mil ciudadanos?

This is the personal a. In Spanish, when the direct object of a verb is a person or a specific group of people like ciudadanos (citizens), you must put an a in front of it.

Why does the sentence use just mil and not un mil for 'a thousand'?

Unlike English, which requires 'a' or 'one' before 'thousand', Spanish simply uses mil. Saying un mil is grammatically incorrect when counting exactly one thousand.

Would it be wrong to say analizan since it refers to many citizens?

Yes, it would be wrong. The subject of the sentence is el censo (the census), which is a singular noun. The verb analiza must match this singular subject, even though it acts upon a plural group of people.