Size and weight is a big decision factor when you are trying to find the ideal camera for your needs.
In this section, We are going to illustrate Nikon D80 and Panasonic FZ100 side-by-side from the front, back and top in their relative dimensions. Nikon D80 has external dimensions of 132 x 103 x 77 mm (5.2 x 4.06 x 3.03″) and weighs 668 g (1.47 lb / 23.56 oz) (including batteries). Panasonic FZ100 has external dimensions of 124 x 82 x 92 mm (4.88 x 3.23 x 3.62″) and weighs 540 g (1.19 lb / 19.05 oz) (including batteries).
Below you can see the front view size comparison of Nikon D80 and Panasonic FZ100. Panasonic FZ100 is 8mm narrower and 21mm shorter than Nikon D80 but it is also 15mm thicker. As you can tell, actually this is not a fair size comparison since Panasonic FZ100 has a built-in lens but Nikon D80 doesn't. Once you put a lens on D80, its thickness will increase significantly.
Now lets look at the top view comparison of Nikon D80 and Panasonic FZ100.
Weight is another important factor especially when deciding on a camera that you want to carry with you all day.
Panasonic FZ100 is significantly lighter (128g ) than the Nikon D80 which may become a big advantage especially on long walking trips.
Again, this comparison may not be very useful in real life as we are comparing the weight of a camera with a built-in lens to the body-only weight of an interchangeable lens camera. Once you put a lens on D80, the total kit will weigh much higher.
Unfortunately neither Nikon D80 nor Panasonic Lumix DMC-FZ100 provides any type of weather sealing in their body, so you have to give extra care especially when you are shooting outdoors. If weather sealing is a must-have feature for you, check these sections: Top DSLR Cameras with Weather Sealing Top Bridge Cameras with Weather Sealing
LCD Screen Size and Features
Panasonic FZ100's 3" LCD screen is slightly larger than Nikon D80's 2.5" screen.
Moreover, Panasonic FZ100 sports a Fully Articulated screen
which you can change the angle and position of the screen almost freely, making it possible to shoot from waist or over the head levels, and especially very useful for shooting selfies and video. On the other hand, Nikon D80 has a fixed type screen which provides almost no flexibility in shooting positions compared to FZ100.