How did the Union Jack combine symbols from England and Scotland?

The Union Jack was created in 1606 to symbolize the union of the crowns of England and Scotland under King James I.12

The design combined the national symbols of both kingdoms:

• The Cross of St. George: The red cross representing England was superimposed onto the Scottish flag.1
• The Cross of St. Andrew: The white saltire (diagonal cross) on a blue field representing Scotland served as the base for the design.31

Because heraldic law prohibits placing a red symbol directly onto a blue background, the red cross of St. George was bordered with a white fimbriation (a narrow border) to maintain proper contrast. This symbolic unification was intended by King James I to bring the two independent kingdoms together into a single state, long before the formal political unification established by the 1707 Act of Union.12