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Style A1 (or Korschelt)
In Europe it is usual to give coordinates in the form of A1 to T19. Where A1 is in the lower left corner and T19 in the upper right corner (from Black's view). The column is given first. Layout.
Note: Historically the letter I is not used to avoid confusion with J.
There are also other coordinate notations in use, e. g. in the form of two figures: 1-1 to 19-19.
In Japanese, coordinates start from the upper left corner. Thus 1-1 is at the upper left corner and 19-19 at the lower right. At least one of the coordinates usually is given in kanji, with the order '(column number) no (rank number)'. For example 10の四 (juu no yon; 10-4) is the upper side star point.
For an example see this game record (a sealed move form in a title match game):
In literature and here on Sensei's Library, points are named by their position with respect to the nearest corner. Symmetrical points collapse. This means there are four 3-3 points and eight 3-4 points. Named points are used for isolated corner analysis. See Named Points.
SGF only uses letters. The first designates the column, the second the row. Start is the left upper corner. For a 19x19 that's aa to ss. At most 26x26 can be addressed: aa to zz (no letter is skipped). Since version 4 this increased to 52x52 by including upper case letters: aa to ZZ. Layout.
This system is very simple to learn and to use. Both axes are labelled as below:
1 2 3 4 5 6 7 8 9 X 9' 8' 7' 6' 5' 4' 3' 2' 1'.
X is of course the Roman numeral for 10. The symbol " ' " is pronounced "prime" when used in mathematics. For example, the point 44' is pronounced "four four prime".)
The benefits of this system are self-evident. Looking at any written coordinate you immediately know what part of the board is referenced. For example, all points on diagonals have the form ii, ii', i'i or i'i'. Similarly, all points ij, ij', i'j, i'j', ji, ji', j'i, and j'i' are in the same position in relation to the corner in their quadrant of the board (taking symmetries into account).
Simple coordinates were invented by Alan Joynt in 2010. They are shared here in the hope that the go community may find this system useful.
In his booklet, R. Schurig uses
- a, b, . . . i, k, i, . . . b, a for the columns, and
- 1, 2, . . . 9, X, 9, . . . 2, 1 for the rows.
He calls the lower left quadrant A, counter-clockwise followed by B, C, and D. Cd4 would be the hoshi in the upper right corner, Cc4 the 3-4 point to its right, and kX tengen. In game records he skips the quadrant qualifier as long it does not change. Points cleared by capture are listed inside square brackets, if not replaced by their number. Layout.
See Audouard coordinates for a different coordinate system more suited to Go.
Don't miss the symmetric Rokirovka coordinates.
Is there one, symmetrical (starting in each corner) and with two characters only (for each point)? Spoiler.
Adding Cardinal Direction to moves. Moves are labeled from 1 - 9 since there are only nine lines to each side. The center vertical is Heaven (Ten) and center horizontal is Origin (Gen). Thus, a 4-4 point could be E4N4 (1st Star Point), W4S4 (2nd Star Point), E4S4 (3rd Star Point), or W4N4 (4th Star Point). Other star-points are E4G (5th Star Point), W4G (6th Star Point), TN4 (7th Star Point), TS4 (8th Star Point), and TG (9th Star Point, tengen), completing the handicap sequence.
To me, it seems more elegant to count from tengen, so that's what I've done in my Coordinate Comparison Game. I also had another idea, which was that cardinal direction (in this case tengen based) could be implemented as squares of kanji.
Our directions are 北 (N), 東 (E), 南 (S), 西 (W). Our numbers are 一 (1), 二 (2), 三 (3), 四 (4), 五 (5), 六 (6), 七 (7), 八 (8). For T we have 天 (first kanji of tengen) and for G we have 元 (origin).
We then compile the kanji into squares, to be read internally in the traditional manner - top to bottom, then right to left. For reasons of convenience, the squares as a group should be read left to right.
For instance, the coordinate comparison game notated in kanji squares:
北西 | 北東 | 南西 | 南西 | 南東 | 北東 | 南西 | 南西 | 南西 | 南西
六六 | 七六 | 五六 | 七六 | 五七 | 五六 | 七七 | 八七 | 六七 | 八五
Suggested by Daniel. Uses 0 - 9 followed by A - I to designate row (first) and column, starting in the upper left corner. Layout.
Just in case you were having trouble memorizing coordinate equivalents by point name.
Western Point Inversion Chart for 19x19 Goban:
1 = 19 = A = T 2 = 18 = B = S 3 = 17 = C = R 4 = 16 = D = Q 5 = 15 = E = P 6 = 14 = F = O 7 = 13 = G = N 8 = 12 = H = M 9 = 11 = J = L 10 = 10 = K = K 11 = 9 = L = J 12 = 8 = M = H 13 = 7 = N = G 14 = 6 = O = F 15 = 5 = P = E 16 = 4 = Q = D 17 = 3 = R = C 18 = 2 = S = B 19 = 1 = T = A