Typesetters will have to use their judgment, after having carefully studied the text of BTS (2.1.1) regarding tables, as well as the examples found there. And it is up to the author to check the proofs, including the layout of the tables. Production editors are also well advised to review complex table layouts.
The aim of a table is conveying data structure and meaning to the reader via juxtaposition and alignment (or spatial arrangement, however you want to call it). The data themselves occupy a certain space as well, some more, some less, and this accounts for part of the design constraints in a table. A well-laid out complex table is quite a feat of design.
There is no way this can be automated satisfactorily following a simple set of rules. It takes a well-trained human to design a good table.
In any table, there are several alignment axes (if we limit ourselves to number columns only; in a tabular matrix with text of equal status and comparable length in all cells, a uniform flush-left alignment will normally produce the most balanced layout):
- The alignment of numbers in relation to each other, from top to bottom. This can be right-aligned, aligned on the decimal point (usually implying an arithmetical relationship between the data in a column), or even centered (this last case is when they do not stand in a direct arithmetical relationship to each other).
- The alignment of a column of numbers within the – usually invisible – boundaries of the column. This can be left-aligned (e.g., when they need to align with the left edge of the column heading), centered (when they need to align with the middle of the column heading) or right-aligned (again, when the column heading suggests it). This alignment of the whole of the number column block within the boundaries of the table column is independent of the alignment of the numbers in relation to themselves: you can have right-aligned numbers lined up at the left edge of the widest number with the left edge of the column header! The influence of the column header on the alignment of the number column block often depends on the header’s width, as well as on the distance between the number column block in relation to columns on the left and right of it. This is something the typesetter needs to consider carefully for each table.
- Note that the alignment of the column headers within their table cells will largely depend on their relative widths.
Compare the examples in BTS 2.1.1 pp. 32-36:
- Tables 6, 7, 8 (pp. 32-33) – numbers aligned right in relation to each other; number column blocks as a whole centered in relation to column headers.
- Table 10 (pp. 34-35) – numbers aligned left, both in relation to each other and to the column headers.
- Table 11 (p. 36) – most numbers aligned right, with column number blocks centered in relation to headers; one number column with numbers centered in relation to each other, and the column number block as a whole centered in relation to the header.
