where是关系副词,在定语从句中充当地点状语,相当there;而which是一个关系代词,在定语从句中充当主语或宾语,相当于一个代词.如:This is the factory -----his father worked ten years ago.在这个句子中,-----his father worked ten years ago部分,缺少了worked的地点状语,所以用关系副词where.再看一个句子：This is the factory -----his father worked in ten years ago.在-----his father worked in ten years ago中,缺少了介词的宾语,所以用关系代词which.
这两个关系词的共同点,都可以修饰表示地点的名词.但where和which的选择,主要根据定语从句中所缺少的成分.如果定语从句中缺少地点状语的话,用where；如果定语从句中缺少主语或宾语的话,用which.
