Which is bigger: 56 cm or 6 cm?
Both 6 and 56 are on the same side of 0 on the number line. 56 is further away from 0 than is 6. So 56 is the 'greater' number.
Mathematically there is a big difference between bigger and 'greater than'. The number that is to the right on the number line is the greater number.
Have a look at:
The further away from 0 is the number the 'bigger' it is. So -39 is bigger than -36 but value wise -39 is 'less than' -36.