1楼的解释有很强的误导性,定语从句用which还是where,并不是由先行词决定的,而是看从句是不是完整.如果从句不完整,缺少名词性成分,要用关系代词which引导,如果从句完整,那么就用关系副词where引导
比如：This is the place which we visited last time.
This is the place where we saw each other last time.
这两句话中,visit是及物动词,所以第一句从句不完整,所以用which.第二句话从句完整,前面用where,虽然先行词都是同一个place.