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 Panasonic ZS1 and Panasonic GF2 side-by-side from the front, back and top in their relative dimensions. Panasonic ZS1 has external dimensions of 103 x 60 x 33 mm (4.06 x 2.36 x 1.3″) and weighs 229 g (0.50 lb / 8.08 oz) (including batteries). Panasonic GF2 has external dimensions of 113 x 68 x 33 mm (4.45 x 2.68 x 1.3″) and weighs 310 g (0.68 lb / 10.93 oz) (including batteries).
Below you can see the front-view size comparison of the Panasonic ZS1 and the Panasonic GF2. As you can tell, actually this is not a fair size comparison since Panasonic ZS1 has a built-in lens but Panasonic GF2 doesn't. Once you put a lens on GF2, its thickness will increase significantly.
Here is the back view size comparison of the Panasonic ZS1 and Panasonic GF2.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Panasonic ZS1 is significantly lighter (81g ) than the Panasonic GF2 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 GF2, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Panasonic Lumix DMC-ZS1 (Lumix DMC-TZ6) nor Panasonic Lumix DMC-GF2 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
Panasonic GF2's 3.00" LCD screen is slightly larger than Panasonic ZS1's 2.7" screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.