From the Dag Hammarskjöld library
The document that describes it
Apparently the design was made by the US Strategic Services office, I'd be curious if there is a name behind the design...
The current United Nations emblem was approved on 7 December 1946. The design is "a map of the world representing an azimuthal equidistant projection centred on the North Pole, inscribed in a wreath consisting of crossed conventionalized branches of the olive tree, in gold on a field of smoke-blue with all water areas in white. The projection of the map extends to 60 degrees south latitude, and includes five concentric circles".