为什么说麦克马洪线没有法律意义？

说麦克马洪线有法律意义不外有2点。第一是麦克马洪先画第二是根据分水岭划界原则。但是清当时一直管辖此线以南一大部分地区。新来者怎么能画一笔就能把地画走了？再说了根据英国自己的法律某人的地（property）被别人实际占有一段时间后就可能属于那人了。更不用说这地一直是大清管辖的。最后这分水岭原则用的也不好引起诸多纠纷。

Adverse possession

https://en.wikipedia.org/wiki/Adverse_possession

Adverse possession, sometimes colloquially described as "squatter's rights",^[a] is a legal principle under which a person who does not have legal title to a piece of property — usually land (real property) — acquires legal ownership based on continuous possession or occupation of the property without the permission of its legal owner.^[1]

In general, a property owner has the right to recover possession of their property from unauthorised possessors through legal action such as ejectment. However, in the English common law tradition, courts have long ruled that when someone occupies a piece of property without permission and the property's owner does not exercise their right to recover their property for a significant period of time, not only is the original owner prevented from exercising their right to exclude, but an entirely new title to the property "springs up" in the adverse possessor. In effect, the adverse possessor becomes the property's new owner.^[2][b] Over time, legislatures have created statutes of limitations that specify the length of time that owners have to recover possession of their property from adverse possessors. In the United States, for example, these time limits vary widely between individual states, ranging from as low as three years to as long as 40 years.^[3]