The amazing Arondissments of Parin and Quận of Saigon

Saigon and Paris are very similar in one regard: the cities themselves are organized into numbered districts.

In Paris a district is called an Arondissment, there are a total of 20 of them, and the districts appear clockwise starting at the center:

In Saigon a district is called a Quận, there are a total of 19 of them, and although the districts start at the center, they are not as neatly clockwise as in Paris:

Why is Saigon similar to Paris? Does this have to do with the history of the French in Saigon? I suppose it does, but I don’t know the details.