I used to be involved in property valuation some years ago what valuers do is :-

1) examine the physical property condition
2) compare previos and latest selling prices (from registrar) of similar property in the vicinity
3) compare advertised prices
4) other relavant info eg. demand vs supply, economic situation etc

Based on all the data that is weighed, the valuation price will be an X value which is what is suggested by the valuer, actually this price is quite subjective and may differ from one valuer to another.