Simply put, an attractive girl can be referred to as a hammer. If the aforementioned female is unbelieveably attractive, she can be called a jackhammer or sledgehammer, accordingly. A place where several hammers coexist can be refered to as Hammer City, or Hammerville, USA.
Your sister is a hammer, but your mom is a sledgehammer (usually said with a pelvic thrusting motion).
You gotta go with us to that bar next week, it's Hammer City over there.
I've never seen her before but she must hail from Hammerville, USA.