Penghu locates on the Taiwan Strait between China and Taiwan in asia. It is the only island county of Taiwan. When the time of low tide comes, more than one hundred isles appear. Therefore, the number of the total isles varies. At a rising tide, there are, generally speaking, 90 isles scattered between north latitude 23^o47'to 23^o 9' and east longitude 119^o18' to 119^o42'. The utmost east isle is called "Chamo isle" , the utmost west isle is called "Hua isle", the utmost south isle is called "Cimer isle", and the utmost north isle is called "Mudow isle". The utmost west isle is also the utmost west boundary of Taiwan. Another unusal thing about Penghu isles is that the tropic of cancer goes through the "Hoojing isle" , one of the 90 isles.