～を中心に— With This At the Core

• この店は若者を中心に人気がある。

  Kono mise wa wakamono o chuushin ni ninki ga aru.

  This shop is popular mainly among young people.

  若者を中心に marks young people as the central group where popularity concentrates.

• 会議では環境問題を中心に話し合った。

  Kaigi de wa kankyou mondai o chuushin ni hanashiatta.

  At the meeting we discussed mainly focusing on environmental issues.

  環境問題を中心に shows the discussion revolved around environmental issues.

• 太陽を中心として、惑星が回っている。

  Taiyou o chuushin to shite, wakusei ga mawatte iru.

  The planets revolve with the sun at the center.

  を中心として marks the sun as the physical center of the orbits.

• ・を中心とした + noun modifies the following noun ('centered-on X ~').
• ・Works for both physical centers and conceptual main focuses.
• ・Register: neutral; common in explanations, reports, and news.

Commonly confused with

The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones ～を中心に is tested against.

• ～気味 — A Touch Of, -ish
• ～げ — A Look of…
• ～ずじまい — Never Got Around To It
• ～というものだ — That's Truly What It Is
• ～どおり(に) — Just As
• ～として／としては — In the Capacity Of
• ながらに／ながらの — Just As It Is / While Remaining
• にかかわる — To Concern / A Matter Of