I have a clear idea_____everything is located on the surface of the globe.这里为什么要用where 啊？

I have a clear idea (of/about) where everything is located...我对于每样东西在地球/球体表面的什么位置有清楚的概念。/我很清楚每样东西在什么地方。
干嘛问2次呢？