沿 means “run along, follow”

そう · sou

Also: run alongside, follow along, lie along

Kun'yomi (Japanese reading)
そう
On'yomi (Chinese reading)
エン

JLPT N1 · Taught in grade 6 · 8 strokes

The story

Water (氵) beside ridges (几) over a hollow (口): a stream slipping out between them, following the river down. 沿う is to run alongside: 沿線 is the area along a train line, and crowds on the 沿道 cheer the Hakone Ekiden runners every January.

Used in 沿う (sou, to run along/follow), 沿線 (ensen, along a rail line), and 沿岸 (engan, coast)

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Readings from KANJIDIC2, © EDRDG, CC BY-SA.