Source: Tom Whittaker, S.V. Medaris, and Steve Ackerman.
Air density has a significant effed on how far a fly ball will travel. The same pitch (speed and angle) can travel different distances depending on the location of where was hit. The images show the difference between the same pitch hit in New York (Elevation: 55 ft.) versus Pike's Peak (Elevation: 14,109 ft.).
Click on the link provided below the images to explore the relationship between air density and fly balls by changing the location of the stadium, and angle and speed of the pitched ball.