Been looking to start your own square foot garden? It's a great concept that is extremely popular in the US.
Apart from the fact that the whole system is based on imperial measurements, it's really easy to do and work with.
The decision to go for 1.2m square rather than 1m is in recognition of the growing following for the square foot gardening principles. 1.2m is basically 4 feet, which is the recommended size to create a 4 foot square garden. This space is then divided into 16 x 1ft squares. It's a great gardening system and if you are not familiar with it I recommend having a look at the creators website http://www.squarefootgardening.com.
List of veggies and herbs and the ideal plant spacing
Once you have had your square foot garden for a while you will learn what sizes plants grow too, then you will be able to plant just about anything and know what spacing to use dependant on their final size.