To be sure, you should:
* Consult your owner's manual: This is the best resource for the exact location specific to your vehicle's engine.
* Look online for a diagram: Searching for "2003 Ford Focus coil pack location [Zetec/Duratec]" (replace with your engine type) will likely yield images and diagrams showing its position.
Without knowing your specific engine type, pinpointing the location more precisely is difficult. But the "on top, near the center" is a good starting point for your visual search.