No two people will see the same rainbow. If one imagines herself or himself standing at the center of a cone cut in half lengthwise and laid on the ground flatside down, the raindrops that bend and reflect the sunlight that reach the person's eye as a rainbow are located on the surface of the cone. A viewer standing next to the first sees a rainbow generated by a different set of raindrops along the surface of a different imaging cone.
Using the concept of an imaginary cone again, a viewer could predict where a rainbow will appear by standing with his back to the sun and holding the cone to his eye so that the extension of the axis of the cone intersects the sun. The rainbow will appear along the surface of the cone as the circular arc of the rainbow is always in the direction opposite to that of the sun.