Flag designs exhibit a number of regularities, arising from a variety of practical concerns, historical circumstances, and cultural prescriptions that have shaped and continue to shape their evolution.
First among the practical issues confronting a vexillographer is the necessity for the design to be manufactured (and often mass produced) into or onto a piece of cloth, which will subsequently be hoisted aloft in the outdoors to represent an organization, individual, or idea. In this respect, flag design departs considerably from logo design: whereas logos are predominantly still images to be read off a page, screen, or billboard, flags are alternately draped and fluttering images to be seen from a variety of distances and angles. The prevalence of simple bold colors and shapes in flag design attests to these practical issues.
Flag design is also a historical process in which current designs often refer back to previous designs, effectively quoting, elaborating, or commenting upon them. Families of current flags may derive from a few common ancestors as in the cases of the Pan-African colors, the Pan-Arab colors, the Pan-Slavic colors, and the national flags inspired by the flag of Turkey.
Certain cultures prescribe the proper design of flags, through heraldic or other authoritative systems. In certain cases, prescription may be based on religious principles; see, for example, Islamic flags. As a discipline, vexillology is beginning to promote design principles based on a body of research on flag history and design. Prominent examples are Ted Kaye's five Good Flag Bad Flag principles published and endorsed by the North American Vexillological Association:
Keep It Simple: The flag should be so simple that a child can draw it from memory.
Use Meaningful Symbolism: The flag’s images, colors, or patterns should relate to what it symbolizes.
Use 2–3 Basic Colors: Limit the number of colors on the flag to three, which contrast well and come from the standard color set.
No Lettering or Seals: Never use writing of any kind or an organization’s seal.
Be Distinctive or Be Related: Avoid duplicating other flags, but use similarities to show connections.