The plans unveiled this week aim to break down the busy road and rail barriers and create tree-lined walks and green landscaping.
Alsop's vision seeks to redesign transport routes in the town, which the London Borough of Croydon said is "dissected by virtually impenetrable dual carriageways and railway tracks".
This will make significant land available for homes, shops, office and commercial space alongside a public realm of squares and parks.
Alsop said: "Croydon now has a masterplan to transform itself into London's third city." Cabinet member for regeneration Tim Pollard added: "We chose Alsop because he has a reputation for coming up with something out of the ordinary."