A quick escape from Camel City
For the Camel City evacuation procedure to function, the GM must agree that a creature can take any number of free action mount or dismount actions in a turn.
In Camel City, every Medium inhabitant is given a 150-gp camel. Every inhabitant has Ride as a class skill and at least 1 rank in the skill Ride, so every inhabitant is trained. Every inhabitant has the feat Skill Focus (Ride) and the trait Dromedary Warrior. Every inhabitant's Ride skill bonus is +7 (+11 when using cover, fast mount or dismount, and spur mount on a camel).1
When the signal's given to evacuate, inhabitants take from their stables their camels and park them alongside their neighbors' camels, making a line of camels to the prearranged location of the teleportation circle.
At the start of each inhabitant's turn, each takes a free action to take 10 on a Ride check (DC 20) to fast mount a nearby camel followed by a free action to take 10 on a Ride check (DC 20) to fast dismount that camel except on the camel's opposite side, further down the camel line, and repeats this process as necessary until the circle is reached.2 Assuming the circle functions like a location trap, each inhabitant can exit the circle's designated arrival spot by taking a full-round action to run, clearing the way for future arrivals.
For their own safety and the safety of others, all inhabitants of Camel City must be size Medium. (Medium camels being typically unavailable.)
1 A Ride bonus of +10 can be achieved without the trait Dromedary Warrior by instead equipping each inhabitant with a masterwork tool for the skill Ride (50 gp; 1 lbs.) and an appropriately compatible trait like Beast Bond or Savannah Child (the former granting a +1 unnamed bonus on Ride skill checks and the latter a +1 trait bonus on Ride skill checks). Doing so allows the city to accept Small inhabitants but forces such inhabitant along their own exit routes, likely creating enclaves of exclusively Small folk. Further, this costs the city more money.
2 Free actions says that "there may be limits to the number of free actions [a creature] can perform in a turn," and the FAQ agrees (although it was once more specific as evidenced in this 2013 thread).