を中心(ちゅうしん)に

When combined with nouns, the expression を中心(ちゅうしん)に indicates that something is being 'focused on' or 'centered around'. Occasionally, it may also be translated simply as 'mainly (A)', or 'most notably (A)'. 中心(ちゅうしん) itself is a noun that expresses the 'pivot', or 'central focus point' from which something else is occurring. The case marking particleに just marks '(A) を中心(ちゅうしん)に' as the target that is being focused on.

• あのアイドルは若者(わかもの)を中心(ちゅうしん)に人気(にんき)を集(あつ)めている。
  That idol is gaining popularity, mainly among young people.
• 私(わたし)は今(いま)日本語(にほんご)の文法(ぶんぽう)を中心(ちゅうしん)に勉強(べんきょう)をしています。
  Currently, I am focusing my studies on Japanese grammar.

Due to 中心(ちゅうしん) itself marking a 'central point', it may also be used just to express the middle of something, rather than something that is being concentrated or focused on.

• 明日(あす)からは札幌(さっぽろ)を中心(ちゅうしん)に大雪(おおゆき)が降(ふ)るところがあるでしょう。
  There will be heavy snow in some areas, mainly in Sapporo, starting tomorrow.

By adding する in either its dictionary or past forms, を中心(ちゅうしん)にする or を中心(ちゅうしん)にした may appear before another noun. This will highlight the noun that comes after as being the overall thing through which the 'focus on (A)' is taking place.

• この業界(ぎょうかい)ではお客様(きゃくさま)を中心(ちゅうしん)にすることが一番(いちばん)重要(じゅうよう)なことだと言(い)われている。
  It is said that the most important thing in this industry is to focus on the customers.
• これからはクライアントの提案(ていあん)を中心(ちゅうしん)にした話(はな)しを進(すす)めたいと思(おも)います。
  From now on, I would like to proceed with a focus on the client's proposal.
• ここはスケートボードを中心(ちゅうしん)にしたポップアップストアです。
  This is a pop-up store focusing on skateboards.

Additionally, the case-marking particle と may sometimes replace に. This change will put more nuance on the focus point being conclusive, rather than progressive or decisive.

• 健康診断(けんこうしんだん)に行(い)ったら先生(せんせい)に揚(あ)げ物(もの)を中心(ちゅうしん)とする食生活(しょくせいかつ)はやめるようにと言(い)われた。
  When I went to my physical check-up, my doctor told me to stop centering my diet around fried food.