The official pdf document (by Israel) can be read here:
I've included some captures from the document about launch sites. In the document Israel lists around 7-10 "illegal" launch sites out of a thousand. Here's a breakdown:
Rocket sites from the north, middle and south in Gaza.
It looks evenly distributed to me. After their rockets are launched the only thing remaining is a tripod holding the rocket and not the militants themselves. There is no need to aerial bomb every building next to an empty tripod. It accomplishes nothing. Make peace.