Movement detection in space


I need an advice for tracking movement. I need to detect movement of people in a big space. It doesn’t have to be very precise I just want to visualize where in space how many people move (a cloud at the movements position, more dense the more movement around that spot or something like that). I thought about kinect and using the number of detected skeletons but the range would only be 0-6 if I understood the limits correctly and it’s not even necessary to detect individuals for me. Maybe camera tracking with 2-4 webcams?
The space is a gym with people (up to 250) sitting along long tables on benches. During the event they are able to stand up and move around and in the breaks there will be even more movement. That movement I’d like to roughly detect and make a visualization on a 2D plan of the space.
I’m thankful for any advice and shared experience.