What is the estrato system and why does it matter?

Estrato is a 1–6 socioeconomic rating assigned to each address that determines how much you pay for utilities (water, gas, electricity) — higher estrato subsidizes lower. A 6 apartment can have noticeably higher utility bills than a 3 in the same city. Ask the estrato before signing; it is a real monthly cost difference, not just a status label.