We have lots because we live amongst fields with field drainage farm buildings only 100 yards away. The most humane way we have found is to shoot them, but we do have to resort to rat poison I'm afraid. The cage traps just didn't work for us. Rats are clever creatures.
If you live in a town contact your local council. Country rats are usually not tackled by local councils unless they are actually in your home.
We get them in our loft. They climb up the brick and flint walls!!
A Jack Russell terrier helps!!