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 Nikon S4000 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). Nikon S4000 has external dimensions of 95 x 57 x 20 mm (3.74 x 2.24 x 0.79″) and weighs 131 g (0.29 lb / 4.62 oz) (including batteries).
Below you can see the front view size comparison of Nikon D80 and Nikon S4000. Nikon S4000 is clearly the smaller of the two cameras. Its body is 37mm narrower, 46mm shorter and 57mm thinner than Nikon D80. As you can tell, actually this is not a fair size comparison since Nikon S4000 has a built-in lens but Nikon D80 doesn't. Once you put a lens on D80, its thickness will increase significantly.
Weight is another important factor especially when deciding on a camera that you want to carry with you all day.
Nikon S4000 is significantly lighter (537g ) 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 Nikon Coolpix S4000 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 Compact Cameras with Weather Sealing
LCD Screen Size and Features
Nikon S4000's 3.00" LCD screen is slightly larger than Nikon D80's 2.5" screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.