The cross signifies PA's origin as an English colony. The black and white color scheme and the circles within the cross are taken from William Penn's family crest. Here, the five circles represent the five geographical regions of the state: the Erie Plain, the Allegheny Plateau, the Ridge and Valley, the Piedmont Plateau, and the Coastal Plain. The canton in the upper left consists of alternating quarters of blue and gold, the state's colors, over which is centered a countercharged keystone, a symbol of the state since the Revolutionary War. Though the nickname "The Keystone State" cannot be traced to a specific individual, the nickname stuck because of the role Pennsylvania helped to play in forging a union out of 13 oftentimes fractious colonies with dissimilar economic and political interests. Because of its geographical location, and because its industry and agriculture bore similarities with both southern and northern colonies, Pennsylvania was uniquely positioned to play the role of the keystone that held the fledgling union together. In an analogous manner, in this flag, the disunity of the starkly contrasting alternating quadrants is brought into visual union and harmony by a keystone comprised of equal parts of blue and yellow.