当定语从句中缺少地点状语时，关系词只能用where，而不能使用that。当定语从句缺少表示地点的主语或者宾语，而不是地点状语时，关系词使用that或者which，而不使用where。

如：This is the city where I stayed last year。定语从句I stayed last year缺少地点状语，用where 等于 in which 等于 in the city等于This is the city that I stayed in last year。定语从句I stayed in last year中，in后面缺少宾语，用that，不用where。