I am, in a way, half of eight
but not four - not that straight.
I am, in a way, half of infinite
Refers to its shape, not a straight half of an eight because it is tipped over on its side
my location is always definite.
Probably refers to the tilde being used as root location in a URI, or to the tilde being in the same location below the escape key on different keyboard layouts.
I can mean not only not positive for a logician
but also almost or similar for a mathematician
A symbol similar to a tilde is used in mathematics and logic to indicate negation, inversion, also used to denote estimations and can mean equal to.
My origin is of Spain or Portuguese
It came into English from Spanish/Portuguese, where it is used as an accent placed over Spanish n when pronounced ny (as in señor) or Portuguese a or o when nasalized (as in São Paulo)
its so easy, so please figure me out of these.
I think I did..
Just noticed the title "You are almost there"
Which hints that the tilde is used to denote an estimation