（その）一方（で）
On the other hand, meanwhile (two parallel sides)machine translation
FormationVerb / い-adjective in plain form + 一方（で）; な-adjective + な一方（で）; noun + である一方（で）; sentence-initial: その一方で
〜一方で（いっぽうで）places two SIDES of the same thing, or two contrasting facts, next to each other: 都会は便利な一方で、生活費が高い (the city is convenient; on the other hand, living costs are high). The two clauses don't negate each other — both are true; they're simply two different aspects.
At the start of a new sentence, use その一方で: end the previous sentence, then open the next with "meanwhile, on the other hand." This is a style much favored in journalism and essays when comparing two trends: 輸出が増えている。その一方で、輸入は減っている.
Don't confuse it with 〜一方だ at the END of a sentence — that pattern means "keeps on going (in one direction)" and is a separate grammar point. Also distinguish it from のに・ながらも: those two carry a concessive sense of "although A, B," while 一方で is neutral, simply laying the two sides out in parallel for the reader to weigh.
Examples
都会は便利な一方で、生活費が高いです。
The city is convenient, but on the other hand the cost of living is high.
兄は厳しい一方で、優しいところもあります。
My older brother is strict, but on the other hand he has his gentle moments.
姉はよく働きます。その一方で、遊ぶ時間も大切にしています。
My older sister works hard. At the same time, she also values her time for fun.