Magma is a mixture of melted or semi-molten rock, volatiles and masses that are found below the surface of the Earth and is assumed to exist on different terrestrial planets and some real satellites. Besides melted rock, magma may also comprise dissolved crystals, suspended gas and seldom gas bubbles.
A road map shows you the routes you can take from point A to point B. A topographic map shows altitude by contour lines. So the main difference is directions vs altitude.