whose map is that? 谁是主语

That 是主语。
那是谁的地图。

正常的句子应该是：
That is whose map?
但特殊疑问句要变结构顺序，所以是
Whose map is that ?

that是主语

is 是谓语
map是宾语
whose是修饰成分，表明所有格形式

map
变成陈述句that is whose map ？
map是主语

That 是主语。