For hundreds of years, the default board size for Go has been 19x19 lines and this is the size almost every player will expect to play on.
This size gives a good balance between the easily secured territory below stones on the third line (72 on the first line plus 64 on the second line, 136 points total) and area in the centre above the fourth line, for fighting (an 11x11 rectangle, 121 points total). Thus the strategies of territory-taking and whole-board fighting can both be effective.
- There on the Go board are 360 intersections plus one.
- The number one is supreme and gives rise to the other numbers because it occupies the ultimate position and governs the four quarters.
- 360 represents the number of days in the lunar year.
- The division into four quarters symbolizes the four seasons.
- The 72 points on the circumference represent the five-day weeks of the Chinese lunar calendar.
- The balance of Yin and Yang is the model for the equal division of the 360 stones into black and white.
-- from "The Classic of Go" by Chang Nui, published around 1050
Interesting coincidence concerning "19x19": The Baha'i religion divides the year into 19 months, while each month contains 19 days - they add 4 days apart to celebrate the new year . This division derives of the Baha'i belief in the importance of harmony and a high meaning they believe the number 19 has.