Expressing concurrency


> 人口が増える [ に伴い／とともに ] 周辺もにぎやかになってきた。  
>  Jinkou ga fueru (ni tomonai/to tomo ni) shuuhen mo nigiyaka ni natte kita

Both the options seem grammatically correct. What's the difference then? Or do
I understand it wrong?




AFAIK, they are nearly identical and interchangeable. One of my grammar books
has the exact same wording for both structures.

> _～すると、それと一緒に_  
>  動詞の辞書形／名詞 ＋ {に伴って・とともに}

参照: [Proportion and Rate](https://japanese.stackexchange.com/q/2528/78)

