Why it looks like this

The French rebuilt Saigon after 1859 as a colonial showcase: a grid of wide boulevards, the opera house, the post office, tamarind-shaded streets near the Saigon River. A few kilometres southwest lay Cholon — 'big market' — the Chinese trading city, denser and older in pattern; the two grew until they touched.

The map's finer grain is the hẻm: narrow alleys, often just a metre or two wide, that branch and branch again behind every main street. Most of the city's people live in these alley networks, invisible from the boulevards.