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Sector Layout

Tony Dziepak, October 1997, last modified 22 May 2009; thanks to George Kleeman for some corrections.


Materials

A quick, attractive indoor sector can be laid out with athletic tape. You can do the sidelines as well as the arcs. Plan on using at least one full roll for each of the sidelines, and for each arc. Standard-width athletic tape is not quite 50mm (regulation) wide, but it shows up well, especially against artificial turf. Also, it is removable. You could also use extra-wide athletic tape.

Outside, you can use paint or chalk, just like any playing field. You can also use the removeable plastic or fiberglass ribbons that are held in place by large staples pushed in the ground. Regulation width is 50cm or 2 inches, but most lime spreaders are set to put down a 4-inch line. This is OK, but I wouldn't go any wider than that. You can get an inexpensive spray paint rolling marker that uses standard spray paint cans.

The sector size:

IAAF, USATF, NCAA, and NFHS sectors all now use 34.92 degrees for shot, weight, discus, and hammer. In indoor competition, where space requires, IAAF and USATF allow the shot sector to be further narrowed by two parallel lines that are at least 9 meters (29'6 1/2") apart. The lines have to be centered on the sector so that equal areas on both sides of the sector are chopped off. Thus the sector lines of the narrowest possible sector follow a "35"-degree sector out to 15 meters from the center of the circle (throwing distance of 13.93 meters), then kink in to parallel lines 9 meters apart. Of course, you could also have parallel lines 10, 12, or more apart where space permits.

Making the sector:

This is the procedure for laying out a 34.92-degree shot sector. Other sectors are done similarly. You need two additional people and at least a 100-foot tape. Hold the tape end in the center of the circle. Have Person A take the spool and walk "out," along with Person B, about 30 feet along where the left sector line will be. Person A stays there, holding the tape at 30 feet. Then Person B walks "across" the center of the sector to about where the right sector line will be. You also walk out and greet Person B at this point. Person B stays there and holds the tape at 48 feet. Then you walk the spool "back" to the center of the circle.

You should end up with you holding the tape at the 0 mark and the 78-foot mark standing in the middle of the circle. Person A is holding the 30-foot mark, and person B is holding the 48-foot mark. Now all 3 of you have to pull tight to form an equilateral triangle, with each person at a corner. You can rotate this triangle about the center of the circle until you have it where you want it, but make sure the volunteers keep the hold of their tape at 30 feet and 48 feet.

Keep in mind that these marks are just to lay out the circle; they don't indicate a throwing distance of 30 feet because they originate from the center of the circle, whereas throws are measured from the inside of the toeboard.

Double check the center of the circle: the tape along the left sector line should intersect the inside edge of the toeboard at exactly 3'6", and the right tape should hit the inside edge of the toeboard at 74'6". If it is off, move the 0-78' spot until these marks are aligned.

Use a 100-foot or 30-meter tape for shot and weight; use at least a 165-foot or 50-meter tape for discus, hammer, or javelin.

If you want the sector to be exactly centered on a line, then rotate the triangle until the midpoint of the tape segment between Persons A and B intersects the center line. It is important that the sector is centered on the toeboard for shot, and the sector should be centered on the cage for the discus and hammer (the permanent part--not including the swing doors, if any). This is more important than centering the sector on the outer rectangular slab in which the circle is poured.

Now when you have your sector aligned where you want it, stake or mark hash lines on the grass near the circle, and another hash near persons A and B. Mark these hashes on the outside edges of the tape measure. Remove the tape, then run a string line connecting the inside edges of the hash lines. then paint the line on the outside edge of the string line.

While you are at it, mark the sector on the concrete pad outside of the circle rim. This is used as an indication of where you want your sector to be aligned. Extend the string line across the circle and stake behind the circle. The inside surface of the circle should not be painted.

The math

Whatever angle sector "x" you want to put down, the cross distance is 2(sin(x/2)). So, for example, in a 40-degree sector, the cross distance is 2(sin20), or .684 times the sides. In English, this means if you go from the center of the circle down the left sector line 10 meters, then go across to the right sector line to 16.84, and return to the center of the circle along the right sector line to 26.84.

Javelin sector and runway: A javelin sector is even narrower; it is always the same for all levels of competition: high school, college, USATF, and IAAF. The sector sides are twice as long (.5) as the length across. You can go 0-20-30-50 meters or 0-60-90-150 feet. The javelin runway is 4 meters wide, and the sector originates from a point in the center of the runway 8 meters behind the foul arc. See the IAAF or USATF rulebook for more details and a diagram on how to layout a javelin sector.

Here is a summary table of all of the sector measurements:

                                  Across  Hold the tape (feet)  Hold the tape
degree who uses it                ratio   out-across-back       (in meters)
28.96  all JT                     0.5     60'-90'-150'          20-30-50
34.92  all except some HS 2006    0.6     30'-48'-78' OR        10-16-26
(+parallel lines: IAAF indoor SP)         60'-96'-156'          20-32-52 or 15-24-39

Additional angles for some high schools in 2006 only:
65.5   some HS SP                 1.082   30'-62'5.5"-92'5.5"   9-18.74-27.74
60     some HS SP,DT              1.0     30'-60'-90' OR        10-20-30
                                          60'-120'-180'         20-40-60 or 15-30-45
47.16  some HS SP, discus (MO)    0.8     30'-54'-84' OR        10-18-28
                                          60'-108'-168'         20-36-56 or 15-27-42
45     some HS SP,DT              0.765   30'-52'11.5"-82'11.5" 10-17.65-27.65
                                          60'-105'11"-165'11"   20-35.31-55.31
40     some HS SP,DT (CA);        0.684   30'-50'6.25"-80'6.25" 10-16.84-26.84
                                          60'-101'0.5"-161'0.5" 20-33.68-53.68


Distance arc measurements

Arc measurements enable throwers, officials, and spectators to get a ballpark estimate of distance thrown as soon as the implement lands. Arcs may also be used to indicate minimum, qualifying, or record distances.

To do arcs, get someone to hold the tape at the center of the circle, and add the distance from the center of the circle to the rim or toeboard. For example, if you want to put down a 40-foot shot put or weight throw arc, you want to put the inside edge of the line at 43'6". For a 15-meter line, measure 16.07. So for shot, weight, and hammer, add 3'6" or 1.07 meters. For discus, add 1.25 meters, or 4'1.25". For javelin, your foul arc will be at 8 meters, and you will add 8 meters for all of your distance arcs. For example, measure out 58 meters to represent a throwing distance of 50 meters.

Sometimes you want to put some lines down for both hammer and discus where you throw it from the same concentric circle. In this case, I would put the CENTER of the line down adding 1.16 meters, or 3'9.75". Then for hammer, the inside of the edge of the line represents approximately the distance; whereas for discus, you need to throw over the line to reach the represented distance. When do you want to fudge like this? When you are using spray paint, or time or personnel constraints do not allow you to adjust all of the arcs by 18 centimeters.

Regulation is to use white lines for the foul lines, and convention is to also use white for the regular measurement arcs, but you can use colored arcs or hashes to represent record distances (school, track, world, national, meet records, or NCAA qualifying distance, or minimum measurement).

You can also use dashed lines. For example, Suppose you have a shot sector with arcs every 5 feet from 40 feet to 60 feet. If they were all solid lines, sometimes one can lose track of which line is which. I like to make every other arc (the 45-foot arc and the 55-foot arc) dashed lines.

I like to put down lines that would be relevant to each competition, if possible. For example, if there is time between the men's and women's events, add or take out appropriate arcs. If the entry form is available indicating the best marks of the competitors, use this to determine which lines to put down. It is exciting when the top thrower throws over the furthest line, so, for example, if the top 2 shot putters have thrown 56'1" and 55'9, then the last line would be 55'. I wouldn't put down 60' because they are not going to reach that. If one of the throwers requests it, I would put down a one-foot hash mark at 60', down the center of the circle, but not an entire arc. Now, if the best thrower is hitting 59'2", I would put down the 60' line.

On the other end, I wouldn't bother with any arcs lower than the lowest entry mark. If there is a minimum marking distance, of course, you would put that down so that the official knows what marks not to record.

Related article: Overlapping sectors

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