This was my husband's creative space filling idea - but see since I am the holder of all the patience - I was naturally selected for it's timely execution.
To start off you need to find the centre of the space you would like to fill. Pick a spot and poke a pin in - tie a string to the pin and have the other end tied to a pencil - shorten or lengthen your string according to the size of the circle you are keen on. Draw a circle.
Use a level or something else that works for you, to find the four 1/4's of the circle. Mark them off. Now this is where I get Math ghetto on ya. I do not know Algebra. I know my version and it did me right. What you need to figure out next is how much space to put between each nail. I took a piece of string - ran it along one 1/4 section and measured the string I used on a soft sewing measuring tape. I divided that amount by the total number of nails I wanted to use in each section. Like this: String length was: 64.5 and I wanted to use 15 nails = which equals 4.3 cm between each nail. (I did find that on my last nail of each section I had a odd amount of cm's - but just divided it up the best I could and it made no difference to the design outcome)
Once all of you nails are in the fun begins! Pick two nails on opposite sides of your circle (tie one end to a nail) - by no means does it have to be exact or even close to even sections. Start stringing your yarn back and forth - left side of one and right side of the other - you can go fully around or stop wherever it pleases your eye. Go crazy! Try new starting points and layer it up! There is honestly no right or wrong to this design feature - don't like it? - take it down and try it again!