Additionally, when it comes to in and at and places, the semantics can be broken down as follows:
 inside a location
- in Fatehpur neighborhood
- in Nimba
- in the valley
- in Kirtipur city
- in the town of...
 a location, neither inside nor outside. Just a point in space.
 at + time
- at [these locations] Bootan Mandi, Model House, Bhargo Camp, ...
- at the venue
- at Lac Residents of #3b District in Grand Bassa County
- at 8 p.m.
- at night
- at sunset
- at dawn
- at this time
So, given the function and distribution we just saw, that curfews can be described as imposed inside a location, at a point in space, and at a point in time, the following hold true:
Ex: The police officials imposed curfew in(side) the place where riots took place.
Ex: The police officials imposed curfew at the place where riots took place.
Determining which preposition is best, in or at, depends on several factors.
i. Does the writer feel the verb phrase impose curfew takes in for locations and at for time? If so, then in would be the correct choice above.
ii. Does the writer feel the verb phrase impose curfew is compatible with both prepositions, in for inside and at for a point in space? If so, then both would work as the correct choice above. Their semantics, however, would be slightly different.
iii. Does the writer believe the preposition in modifies a specific noun, whereas at modifies a non-specific noun; e.g., in the town of... ; at the place where? If so, then at would be the correct choice above.