Over time, usage has evolved. Some football broadcasts change the color of the line from yellow to red on 4th down, or show a second computer-generated line (usually blue in color) that marks the line of scrimmage. Lines can also be projected to show other types of field position, including markings for the red zone and the optimum maximum distance for a placekicker's statistical field goal range. In extreme weather situations, an entire virtual field with yard and boundary markers can be projected onto the field in order to allow league officials, broadcasters and viewers some way to follow action when all field markings are obscured by snow, fog or mud.