Electric field vectors can be added like any other vectors. If we had two source
charges, their fields would overlap and effectively add; a third charge wandering
by would feel the effect of the combined field. At each position in space, add the
electric field vector due to one of the charges to the electric field vector due to the
other charge: Etotal = E 1 + E 2. (This is superposition again.) In the following
diagram, E 1 is the electric field vector at a particular location due to the charge
+Q, and E 2 is the electric field vector at that same location due to the other charge,
−Q. Adding these vectors gives the overall field vector Etotal at that location.
If this is done at enough locations, we can sketch the electric field lines.