For instance consider the
map of the Rawah Wilderness on the right.
All points on the same line are at the
same elevation, just as all points on the
same equipotential lines are at the same
voltage. Water will always flow
downhill,hence the rivers are always
perpendicular to the lines on the
topographic map, similar to the way
electric field lines are always
perpendicular to equipotential lines.
When lines are close together, the slope
is steep, e.g. a cliff, just as close
equipotential lines indicate a strong
electric field. Lakes are at the same
elevation, in the same way conductors are
at the same potential.