The
gtol.sym file has a section at the top explaining the format and units used for making symbols.

In the file, categories of symbols are grouped together and each category contains multiple libraries and symbols.
Libraries are formatted as: #<Name of library>,<Description of library>.
Symbols are formatted as: *<Name of symbol>,<Description of symbol>.
Lines beginning with “A” define a portion of the geometrical shape of a symbol. Symbols often have more than one of these rows.
BOUND is a control variable for symbols in the gtol.sym file. BOUND controls horizontal spacing of a symbol within a row of text in notes and dimensions.
Semicolons precede commented rows (which are ignored).
Symbols are composed of geometric shapes that can consist of lines, arcs, circles, polylines, and alphanumeric characters. The formats of these shapes are:

Symbols are defined on a 1 x 1 imaginary square grid where 0,0 is the lower-left corner and 1,1 is the upper-right corner. They are not limited to this grid, however. You can also use numbers larger than 1.0 and smaller than 0.0.
Here is an example of a square grid with its coordinates going from 0,0 to 1,1:
An example of how a line is defined on a square grid:
