Kedah is a flat plain except for Gunung Jerai. It was easy for the Japanese to capture Kedah. I visited Kedah to see for myself, and true enough, Kedah is as flat as a pancake and very easy to capture. Even the roads are straight. I passed by the aerodrome and thought for a second, this must be where things happened.
This is the account of the battle that occurred in Kedah:
There's mention of Singora, Jitra, Changlun, etc.