Windmills are known worldwide as an iconic symbol of Dutch culture. Some 1,200 historic windmills survive, most of which are gristmills or polder mills. Many remain fully functional, and their upkeep and operation is promoted by a number of civic organizations, including De Hollandsche Molen, Gilde van Vrijwillige Molenaars and Stichting De Fryske Mole. Several Dutch villages are known for their concentration of windmills, including Kinderdijk, Zaanse Schans, and Schiedam, home to the tallest windmill in the world. Tjaskers, a kind of windmill native to Friesland, were also used for water management.