It usually stands for rivers or borders, depends which map you're looking at.
an equator line
The horizon
It can mean anything but normally it means a river.
A blue line on a map is a lake ,river , or body of water
Water represents a blue line on a map.
The blue line on a map usually represents a stream of water!
a blue line on a map means that it is water weather it is a stream river or lake
The color blue typically represents Europe on a map or flag.
A wavy blue line on a map usually indicates water. I could indicate a river, canal, or any type of waterway.
I am guessing that's a river.
equeater
the blue line represents Lakes, Streams , canal and mainly just water