Using "and" in If(

Its simpler syntax ...

just one IF

IF(

[ship density]<1, 400,

[ship density]<2, 300,

ship density], <4, 250  etc

The conditions get evaluated from top to bottom in sequence and will grab the first result which is true. So you don't really need to have each subsequent condition eliminate the previous ones above.

But if you did want the extra "wordiness" just for your own readability or understanding it would look like this

IF(

[ship density]<1, 400,

[ship density]>=1 and [ship density] < 2, 300,

[ship density]>=2 and [ship density] < 4, 250 ... etc ,