1st things 1st.. gotta get to know the difference between the icons:

<- this is commerce
and

<- this is gold
while it might not seem like a big deal at first glance, it trips up alot of new people. when you see those icons in pop-ups inside the UI... they are not the same.

is generated by tiles and trade routes etc. Each city will generate a certain amount of

which gets put through your research slider (on a per city basis).
the best way to explain how things really work is through example.
New Orleans (where im from

) generates 50 commerce. You have your slider set at 50%

, 0%

, and 0%

. This in effect means that the remaining 50% will go to creating

which is used for paying for your city maintenance and units.
50% of 50 = 25 going to

and 25 going to

.
any scientist or merchant specialists you have in this city will add their +bonus to those two 25's. you now have your base

and base

values for this city. these base values then get multiplied by any buildings you have that have % modifiers.
a library will take your base

and add another 35 percent ontop of it.
a bank will take your base

and add another 50 percent ontop of it.
the thing to remember is this...
your gold creation relates entirely to where you research slider is set. if all three

,

, and

sliders combined = 100%... you aren't generating any

from your

(such as a combined setting of 70%

, 10%

, and 20%

).
since you're going to be running high science rates for most of the game, to get any good use out of your gold multiplying buildings... you're going to need to find a way to get gold directly instead of through your

. that is done through religious shrines, corporations, merchant specialists and what have you. Pile all these up in one city and build all the

multiplying buildings you can in this city. such as banks, markets, grocers, wall street etc. most great merchants you pop will be settled here as well. if you do this really well... you can have your research slider at 100% and still turn a profit in alot of cases.
my last monarch game, my wall street city was generating over 300

per turn with my research set to 100%

. this one city paid for all of my expenses. all other cities focused on science or production.
i did this by having a religion founded there with a holy shrine. made sure to spread that religion around for the direct gold. used lots of farms to run as many merchant specialists as i could (at times i had 10 of them) and then settled any great merchants i popped. built all

multiplying buildings.. including Wall Street. And then later had two corporation HQ's stationed in that city. the city didn't generaate a whole lot of

, but it didn't need to. it was generating the

directly in this city.