Already answered - the BMW is just a different thing altogether.
Bear in mind, once again, gthat the 316i is the absolute basic model with the smallest engine, but it will be like a Rolls Royce in terms of comfort & a Porsche in terms of performance & handling compared to the Ka.
The 316i is much heavier, but is a second quicker to 60 & has a top speed of around 20mph more than the Ka (and you'd be pretty brave or stupid to find out the top speed of a Ka).
The BMW will also be far more reliable & cost less to maintain than the Ford.