lincoln`s father was among the first to settle in(what)is nom one of the most developed areas>
疑问：
为什么用what而不是where或which that?

lincoln`s father was among the first to settle in(what)is nom one of the most developed areas>

what在这里做的是in的介词宾语从名。一般可理解为：what=the thing(place) that .

that 在名词性从句只能做连接作用，是没有词义的

而这里如果是选which where 名词性从句，是除了连接作用外，还保留其疑问意义，语序是陈述语序，如是有必要用疑问语序，必须用it 做形式宾语，如果在这里用疑问语序就是定语从句的结构，但前面又没有先行词，所以不能用。

所以选what 是正确的,可以换成这种来理解就好了。lincoln`s father was among the first to settle in the place that is nom one of the most developed areas>
是不是可以理解为the place 后面有一个定语从句，这样就简单了。