MEXICO CITY — The plan is as big as this mammoth city: Turn a seedy metro hub into Mexico City’s Times Square; clear swarms of feisty vendors and remodel the historic Alameda Central; illuminate the plazas and walkways of a park twice the size of New York’s Central Park.

Mexico City’s government is trying to transform one of the world’s largest cities by beautifying public spaces, parks, and monuments buried beneath a sea of honking cars, street hawkers, billboards, and grime after decades of dizzying urban growth.