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 L31 and Sony NEX-3 side-by-side from the front, back and top in their relative dimensions. Nikon L31 has external dimensions of 96 x 59 x 29 mm (3.78 x 2.32 x 1.14″) and weighs 160 g (0.35 lb / 5.64 oz) (including batteries). Sony NEX-3 has external dimensions of 117 x 62 x 33 mm (4.61 x 2.44 x 1.3″) and weighs 297 g (0.65 lb / 10.48 oz) (including batteries).
Below you can see the front view size comparison of Nikon L31 and Sony NEX-3. Nikon L31 is clearly the smaller of the two cameras. Its body is 21mm narrower, 3mm shorter and 4mm thinner than Sony NEX-3. As you can tell, actually this is not a fair size comparison since Nikon L31 has a built-in lens but Sony NEX-3 doesn't. Once you put a lens on NEX-3, its thickness will increase significantly.
Now lets look at the top view comparison of Nikon L31 and Sony NEX-3.
Weight is another important factor especially when deciding on a camera that you want to carry with you all day.
Nikon L31 is significantly lighter (137g ) than the Sony NEX-3 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 NEX-3, the total kit will weigh much higher.
Unfortunately neither Nikon Coolpix L31 nor Sony Alpha NEX-3 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 Compact Cameras with Weather Sealing Top Mirrorless Cameras with Weather Sealing
LCD Screen Size and Features
Sony NEX-3's 3" LCD screen is slightly larger than Nikon L31's 2.7" screen.
In addition to the size advantage, Sony NEX-3 LCD screen also has a Tilting feature
where you can change the angle of the screen to make it easier to shoot from waist or over the head levels. On the other hand, Nikon L31 has a fixed type screen which provides less flexibility in shooting positions compared to NEX-3.