To draw a clear line between things; to distinguish clearly between two categories or positions.
研究と報道の役割は一線を画すべきだ。
The roles of research and reporting should be clearly separated.
そのブランドはカジュアル品と高級品のラインに一線を画している。
That brand clearly differentiates its casual line from its luxury line.
公私の区別に一線を画することが重要だ。
It's important to draw a clear line between public and private matters.