Equipotential surfaces can be shown as lines in two dimensions to provide a quantitative way of viewing electric potential. Every point on a given line is at the same potential. Such maps can be read like topographic maps.
Below are a set of electric field lines and equipotential surfaces caused by a certain set of point charges (taken from page 588 of the textbook). You can use it to test your skill at determining where the field is strong or weak on the basis of the density of field lines, or on the basis of how rapidly the potential is changing. Note that there should be an infinite number of equipotential surfaces surrounding each point charge; unfortunately their artist got tired of drawing them rather soon.