Question

what consideration have been made while deciding the IDL

Answer 1

following points are taken into consideration while drawing an IDL
1.Direction of travel
2.Current day and date
Accordingly while travelling from east to west of IDL a day is added.
FOR EXAMPLE:While travelling from America to Japan,if it is Thursday 25th December Friday 26th December in Japan.
While travelling from west to east of IDL day remains same .
FOR EXAMPLE:While travelling from Japan to America if it is Thursday 25th December,only should be considered.