We can show that two things are not equal using not + as + adjective + as
When we use this structure, the first thing mentioned is 'less' than the second thing. The order of the things you are comparing is opposite to that used in comparisons with comparative adjectives.
This one isn't as big as the old one.
(The old one is bigger than this one.)
Jenny's new flat isn't as nice as her old one.
(Jenny's old flat is nicer than her new one.)
Paris isn't as big as Tokyo
(Tokyo is bigger than Paris.)
You can contract the subject, the verb to be
in two ways. There is no difference in meaning:
It isn't as big as...
It's not as big as...