How does Shakespeare contrast Venice and Belmont in The Merchant of Venice?

Venice is Shylock's world. Venice is the ceaselessly active center of cut-throat commerce, ruthless business dealings, and hard-won wealth (which apparently buys happiness for no one in Venice). It is a place of religious intolerance and a place where harsh realities intrude incessantly on daily life. No one in the play has a good word to say about Venice.
In her second line in the play, Jessica, Shylock's daughter, might as well be talking about Venice as about her own home situation with Shylock:

JESSICA: Our house is hell. [2.3.2]

Belmont is Portia's world. Belmont carries its wealth with ease. Belmont is peaceful, even idyllic.

LORENZO: The moon shines bright:—in such a night as this,When the sweet wind did gently kiss the trees, . . . [5.1.1-2]

There's music in Belmont—

LORENZO: And bring your music forth into the air.How sweet the moonlight sleeps upon this bank!Here will we sit, and let the sounds of musicCreep in our ears; soft stillness, and the night,Become the touches of sweet harmony. [5.1.61-65]

—as well as singing. [3.2.65-75]
All is well in Belmont. Lorenzo and Jessica elope to Belmont to escape from Shylock's world. [2.4]
Finally, Belmont is where the play ends happily ever after for everybody but Shylock, who nevertheless has his life spared by the Duke, for which he should at least be thankful.