The flag of the United Nations was adopted on October 20, 1947, and consists of the official emblem of the United Nations in white on a blue background. The emblem's design is described as:
A map of the world representing an azimuthal equidistant projection centred on the North Pole, inscribed in a wreath consisting of crossed conventionalised branches of the olive tree; [...] The projection of the Map extends 40° South Latitude, and includes four concentric circles.
-Official Seal and Emblem of the United Nations, Report of the Secretary-General, 15 October 1946
The blue color that appears in the background of the insignia was chosen to be "the opposite of red, the war color". The original color the group chose in 1945 was a gray blue that differs from the current United Nations flag. The globe used in the original design was an azimuthal projection focused on the North Pole with the United States, the host nation of the conference, at the center. The projection used cut off portions of the Southern Hemisphere at the latitude of Argentina which was acceptable at the time, as Argentina was not an original member of the United Nations.
The olive branches are a symbol for peace, and the world map represents all the people of the world.