Population Growth (Golden Rainbow)

What can I do, besides buy population, to gain it more quickly? ie increase immigration?

And on a side note, when people come into my country, does that mean they are leaving a previous one? Can that happen to me?

There is emmigrations and immigrations. Not sure if there's an exact calculation taking it from other countries.

If you have a good setup for your population then they will stay and encourage others to come. Although, the numbers are very small. You can see the figures on your Population page of your country.

Have good health care, education, higher salaries, good transportation and low unemployment.

Keeping a higher health index will prevent people from dying and allow the the population to grow faster than it would with a lower one.

You can trade hi-level workers for low level ones. The exchange rate is based on salary so you get a lot more low-level workers for fewer higher level ones. Of course you need to have a good education system to do this.