Because of the extensive historical use of compass heading names like "north" and "se" (short for "south-east") in PIC and Pikchr, it makes sense that angles should be specified according to compass degrees. North is 0° and the angle increases clockwise so that east is 90°, south is 180°, west is 270° and 360° is back to north again.
C: dot arrow up from C; text " 0°" arrow right from C; text " 90°" rjust arrow down from C; text "180°" below arrow left from C; text "270° " ljust
Even though heading angles are specified in degrees, the arguments to the built-in "sin()" and "cos()" functions are in radians.