Flat spotting on your tyres occurs when a flat patch forms on the rubber of your tyre that makes contact with the ground. This surface of your tyre is commonly referred to as the tyre's 'contact patch'. When your car is parked for an extended period, its weight and pressure put a load on all four contact patches of your tyres.
If your vehicle is frequently used, the contact patch changes every time the car is taken out. However, if it remains parked in the same spot for a long time, the contact patch stays the same. As a result, flat spots occur when the contact patch is the same.