Curling is played within a curling rink on an ice playing surface known as a "sheet" with granite stones. The aim of the game is to have a stone from your team closest to the center of the house, known as the "tee," after all 16 stones have been played (8 by each team). The curler who throws the rock first for his or her team rolls it down the sheet toward the middle of the rink where it must come to rest behind some part of the house. Then the other players take their turns throwing rocks at the same spot on the sheet. The objective is the same for each player: to throw their rock so that it ends up as close to the center of the house as possible. There are two types of centers: open and closed. With an open center, anyone can see what color shirt the curler is wearing. This makes it easier for opponents to plan their attacks. With a closed center, only members of the same team can see each other's shirts. They cannot use this information against each other but it does make it harder to attack blindly. In addition to colors, teams may also designate their own tags to help them identify their teammates during play. These tags can be anything from words written on a tagline to more elaborate schemes, such as those used by the Canadian women's team at the time of its victory in Vancouver in 1990.