on the right track; on the right lines
Used to say that someone's idea, guess, or approach is roughly correct or heading in the right direction. Often appears in the patterns いい線(を)いく or いい線(を)いってる.
See also: いい線いってる
I think his idea is on the right track.
That answer is on the right lines, but explain it in a bit more detail.
Standard kanji spelling for this expression.
Alternative kanji spelling using 良い; less common than いい線.
Rarely used kanji form.
Combination of いい (good) and 線 (line), literally 'a good line'. The figurative sense of being on the right track likely derives from the idea of drawing a line that is close to the correct one.