Cardon Square is the area that is covered by many chess squares and it depends on the position of the pawn and the opponent King. Once learnt how to draw this in imagination, it is easy to visualise it everytime. This helps to avoid tedious calculations and the possible mistakes. It becomes very easy to conclude whether the pawn will queen or will be caught by opponent's King.
Draw the square from the pawn.
Keep the pawn as one corner.
One side of the cardon square is from the Pawn to the queening square.
The queening square is the other corner.
Draw the diagonal from the pawn towards the last rank and to the side of the opponent's King. That square on the last rank is the third corner.
Now that you have got the three corners of the square, it should be possible to imagine the cardon square.
If your opponent's King is outside the cardon square and if it is your move, the pawn can not be stopped if you push it.
Let us see how!
1.a5
Ke7
2.a6
Kd7
3.a7
Kc7
4.a8Q
And wins. The King can not go anywhere nearer. *