The Radar, sometimes refered to as a Minimap, is a user interface element introduced in Super Smash Bros. Ultimate. It appears during a game whenever a fighter is off-screen to keep track of their location and where the blast lines are.
To minimize screen clutter, the radar is not normally visible on screen. When a character is far enough off a stage that the camera no longer follows them, the radar appears in the upper corner of whatever side of the screen the character is on. The radar is a gray, semi-transparent box that represents the blast lines, with a white rectangle inside of it that represents the camera range. All characters appear as diamonds inside this box, colored after their port or team color—CPUs are colored grey and Figure Players are a gradient blue to yellow—with team color taking priority. The radar comes in two different sizes that can be changed in the Options menu: "Small" and "Large" (the default size). An "Off" setting also exists that removes the radar entirely.
The radar's position will not change while it is active. For instance, if a character goes off-screen on the right the radar will appear in the top-right corner. If that character remains off-screen and goes to the far left, the radar will stay in the top-right corner. The radar will, however, change shape depending on the state of the stage, with camera boundaries shown to be shifting as the stage does, where applicable. On stages such as Mario Galaxy and Windy Hill Zone, the entire radar takes on a rounded arc shape, to represent the curved gravity of those stages.
The radar is primarily meant for players to keep track of each other, as it shows their locations relative to each other and the blast lines. The radar helps alleviate instances of players self-destructing by losing track of the location of their character and removes most instances of players hiding off stage, making it easier for their opponent to perform aerial chases and edgeguards.