Size and weight are big decision factors when you are trying to find the ideal camera for your needs.
In this section, we are going to illustrate the Canon A3500 IS and Olympus E-P1 side-by-side from the front, back and top in their relative dimensions. Canon A3500 IS has external dimensions of 98 x 56 x 20 mm (3.86 x 2.2 x 0.79″) and weighs 135 g (0.30 lb / 4.76 oz) (including batteries). Olympus E-P1 has external dimensions of 121 x 70 x 36 mm (4.76 x 2.76 x 1.42″) and weighs 355 g (0.78 lb / 12.52 oz) (including batteries).
Below you can see the front-view size comparison of the Canon A3500 IS and the Olympus E-P1. Canon A3500 IS is clearly the smaller of the two cameras. Its body is 23mm narrower, 14mm shorter and 16mm thinner than Olympus E-P1. As you can tell, actually this is not a fair size comparison since Canon A3500 IS has a built-in lens but Olympus E-P1 doesn't. Once you put a lens on E-P1, 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.
Canon A3500 IS is significantly lighter (220g ) than the Olympus E-P1 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 E-P1, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Canon PowerShot A3500 IS nor Olympus PEN E-P1 provides any type of weather sealing in their bodies, 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
Canon A3500 IS and Olympus E-P1's LCD screens have the same diagonal size of 3.00 inches.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.