Four is the sacred number of Zia, and the figure is composed of a circle from which four points radiate. These points made up of four straight lines of varying length personify the number most often used by the Giver of all good gifts.
To the Zia Indian, the sacred number is embodied in the earth, with its four directions; in the year, with its four seasons; in the day, with the sunrise, noon, evening, and night; in life, with its four divisions--childhood, youth, manhood, and old age. Everything is bound together in a circle of life and love, without beginning, without end.
The Zia believe, too, that in this great brotherhood of all things, man has four sacred
obligations: he must develop a strong body, a clear mind, a pure spirit, and a devotion to the welfare of his people.
Guided by this historic background, the flag of New Mexico was wisely chosen, with the ancient Zia Sun Symbol in red on a field of Spanish yellow. The symbol's proportions are fixed by legislative act, with the four groups of rays set at right angles , the two inner rays one-fifth longer than the outer rays. The diameter of the circle in the center is one-third the width of the symbol.http://www.nmsu.edu/~bho/zia.html