Blue on a map usually denotes water. Blue lines could be streams and rivers.
the Borders
The black lines mean it is a state boundary.
Usually by contour lines, with the river shown in blue.
A wavy blue line on a map usually indicates water. I could indicate a river, canal, or any type of waterway.
A stream,river or another body of water.
There will be several dark lines on a map, illustrating roads, power lines etc, BUT you probably mean contour lines. These are lines of equal altitude and are usually coloured brown for land, or blue for snow or ice fields.
Blue on a map usually represents water. If it is a road map, blue is often the smaller roads.
It usually means water.
Blue lines
blue
Usually they indicate the borders between the states.
Water represents a blue line on a map.