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.

 0°   90° 180° 270°  
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.