Below you can see the front-view size comparison of the Panasonic FZ1000 and Panasonic ZS100. The Panasonic ZS100 is clearly the smaller of the two cameras. Its body is 26 mm narrower, 34 mm shorter and 87 mm thinner than the Panasonic FZ1000.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.