Systematic target market selection

Hi there.

I wonder how SFs approach target market (niche) selection? Do you see systematic approach to market (niche) selection as smth that adds a lot of value or is it more important that a searcher first limits on those areas where he/she can add the most value?

Are there any data providers you recommend for a start to come up with a reliable general overview of markets / market niches / trends and be more systematic?

Thanks in advance.

Peter