The Radar is a HUD part found in the game. It displays the position of players and objectives.
It is found in the top right of the screen and may be toggled in options menu or multiplayer game setup.
The Radar has appeared in all the games, each varying in behaviour and appearance in each sequel. They display enemies, objectives, players. Even showing players outside the range by showing a triangle in the general direction.
It is not indicative in terms of height however.