A path or route; also the course, order, or logical steps toward a goal — figuratively the line of reasoning or plan to solve or explain something.
事件解決の道筋がようやく見えてきた。
The outline for solving the case has finally become clear.
旅行の道筋を地図で確認してから出発した。
We checked the route on the map before setting out on the trip.
複雑な議論は道筋を整理してから発表したほうが分かりやすい。
It's easier to understand a complex argument if you organize the line of reasoning before presenting it.