How do you know which turbo is suitable for application?

i know the compressor maps can tell you, but how?

I read the thing chip put up, but still im not 100% sure how it works.

im assuming the only real way is to have experience of the engine / turbo?

for instance an engine that makes 200bhp in nasp form, how would you use the compressor map to get say 400bhp from a turbo, when you're going to lower the c/r etc?