In addition to dispelling the disproportionate casualty myth, let's also dispel the "most densely populated" myth (courtesy of Alan Dershowitz). The Hamas apologists first claim is that Gaza is so densely populated that 1) Hamas cannot use any "open areas" to shoot from, and 2) the civilians don't have anywhere to go to.
We don't need to dispute the amount of people in Gaza for now. But it is a fact that they are not uniformly spread out. There are some very densely populated areas in Gaza. And there are some open areas, mostly fields with only some scattered buildings. So, there are open areas for Hamas to operate from. Plenty of open areas, in fact. They just CHOOSE not to. For demonstration, I cropped a satellite image of Gaza from Google Maps. The areas I outlined in red are relatively unpopulated, with only scattered buildings. See for yourself. Feel free to look at Google Maps yourself.