What is the difference between 対する and 関する？ For the 'relate' meaning.
These two phrase are fundamentally different. I guess you could loosely translate them both as 'related to' but I will list a few examples that hopefully show how different and not interchangeable they are.
Examples and Differences:
first - the 対 character is often used in words meaning opposition, or contrast (一対一、対立）while the 関 character is often used in words meaning relation (関係、関連）
～に対して： Is defined as toward (as in an attitude toward), in contrast to, in regard to.
～に関して：Is defined as concerning, with regard to, about, on. Can be used similar to について
Americans views regarding Russia... (have become harsh, were incorrect etc.)
I wrote a report regarding Russia's goverment
You can see in these examples that に対して is used to indicate america's views towards Russia, while に関する was used as regarding/about.
As shown in the examples below, に対して cannot be to indicate a pure "about", as in "the class was about space" or "the lecture was about his journey".
Last week, a meeting was held about Tokyo's tax policy.
You could not use に対して in this sentence.
Lastly, に対して can be used to mean "in contrast" where 関して has no such meaning.
In contrast to City A, who's economic situation is very stable, City B's economy is crumbling.