Most of the races over a season are at sea level, however, Mexico and Brazil are at Altitude and have 25% less oxygen.
This causes additional technical challenges for the team's engineers as the Cooling, Aero and Engine Aspiration are affected.
Less air means less cooling, so you will see changes to help improve cooling. These often include larger sidepod intakes and vents added to the bodywork.
As the air is approximately 25% thinner at Autodromo Hermanos Rodriguez, there is less downforce and drag. Teams will typically use a unique rear wing to help compensate for this phenomenon.
The engines require air for asperation and while the current hybrid Power Units require less oxygen than the old V8 and V12 engines, they are still put under additional stress. The turbos work to push through more oxygen but they can not push that hard for a full race.
Fortunately, all teams are facing the same challenge so they are all relying on their technical brainiacs to fine-tune the car to suit the conditions.