在定语从句中,where和in which 在什么情况下不能互用?

开门见山,闲话少叙.定语从句中,只有当定语从句的先行词为地点（或抽象地点）时,关系副词where才能与介词（in/on/at）+ which互换使用.如：This is the factory where/in which I worked for two years.It's helpful ...