The Flag of Israel

The flag of The State of Israel includes two blue stripes on a white background with a Shield (Star) of David (in Hebrew: Magen David) in the center. At the celebration of the third anniversary of the founding of the agricultural village of Rishon LeZion in 1885 it was the first time a blue-and-white flag was raised. Independently of the Rishon Lezion event, a blue-and-white flag was raised in 1891 in Boston at the inauguration of the meeting hall of the Bnai Zion Educational Society. That flag had blue stripes above and below a Star of David that had the Hebrew word "Maccabee" inscribed in its center. Bnai Zion first displayed their banner publicly in October 1892, during festivities to mark the fourth centenary of the discovery of America. This time the word "Zion" replaced "Maccabee". 

The blue color in the Israeli flag is based on a tallit, a religious article of clothing. The exact color of blue meant to be used on the tallit is not known and in fact everything from black to reddish purple is used to symbolize its different religious and political connotations. The most common color (the light blue) comes from the fact that the tallit most people wear is a light blue with the deliberate statement of "this is most probably not the right color". 

The Magen David (shield of David, or as it is more commonly known, the Star of David) is the symbol most commonly associated with Judaism today, but it is actually a relatively new Jewish symbol. It is supposed to represent the shape of King David's shield (or perhaps the emblem on it), but there is really no support for that claim in any early rabbinic literature. In fact, the symbol is so rare in early Jewish literature and artwork that art dealers suspect forgery if they find the symbol in early works. 

The first person in modern times who voiced the idea that blue and white are the national colors of the Jewish people, was the Austrian Jewish poet Ludwig August Frankl (1810-1894). More than three decades before the First Zionist Congress, Frankl published a poem entitled "Judah's Colors": 

When sublime feelings his heart fill,
He is mantled in the colors of his country
He stands in prayer, wrapped
In a sparkling robe of white.
The hems of the white robe
Are crowned with broad stripes of blue;
Like the robe of the High Priest,
Adorned with bands of blue threads.
These are the colors of the beloved country,
Blue and white are the borders of Judah;
White is the radiance of the priesthood,
And blue, the splendors of the firmament.
A. L. Frankl, "Juda's Farben", in Ahnenbilder (Leipzig, 1864). 

Frankl's poem was translated into flowery Hebrew and appeared in the periodical Hahavatzelet (The Rose of Sharon) in 1878. We do not know if the founders of Zionism knew the poem, but it is a fact that the flags of almost all the early Zionist associations borrowed the blue stripes of the tallit. 

The Israeli flag legislation states that the official measurements are 160×220 cm. Therefore the official proportions are 8:11. Since nobody enforces this law, you can find variants at wide range of proportions.

The 1948 Flag Proclamation quoted from the Israeli Ministry of Foreign Affairs Flag and Emblem webpage mentions that: 

The flag is 220 cm. long and 160 cm. wide. The background is white and on it are two stripes of dark sky-blue, 25 cm. broad, over the whole length of the flag, at a distance of 15 cm. from the top and from the bottom of the flag. In the middle of the white background, between the two blue stripes and at equal distance from each stripe is a Star of David, composed of six sky-blue stripes, 5.5 cm. broad, which form two equilateral triangles, the bases of which are parallel to the two horizontal stripes.