The map above (which is linked to the recording) is just one suggestion about how to organize this music.
Note that the numbers refer to 4-bar segments, not to measure numbers.
Most important to the overall structure are: 1) the Minor/Major/Minor division shown by the color changes, and 2) the appearances of the THEME (comprising 2 times through the 4-bar progression) at the beginning,
precisely in the middle, and at the end. The distinctions between "Build" and "Plateau" are obviously more subjective. This happens to be a way I mapped it out for students years ago to give a sense of the overall flow.
Although Bach's use of the symmetrical number 64 is obviously intentional,
it's interesting that the phrase structure isn't quite so neatly divided.
The music begins on beat 2 (in the typical triple time of a chaconne), and you'll see that the first repetition also starts on beat 2.
Beginning with the elided cadence into segment #3, the patterns generally change on downbeats,
though almost always with elided cadences from segment to segment.
Everything else falls into neat 4-bar segments except for the mid-point occurrence of the THEME,
the beginning of which is disguised by continuation of the preceding pattern,
the D Major statement of the THEME, and the final statement of the THEME,
both of which clearly start on beat 2, like the beginning.
Although it is tempting to refer to this as a 256-bar composition, there are actually 256 2/3 bars.
In most editions I've seen, the incomplete first measure is still numbered as 1,
so I've followed that convention.
The notation was generated in Lilypond.
Although there is much about the notation that could still be tweaked,
notice how much Bach demands by sometimes showing four varied voices on one staff.
Measures such as #12 and #13 are quite awkward!
The arpeggiated patterns in segments 23-30 are simply notated as chords in Bach's original,
but seeing all of the fast notes written out helps to show the rhythmic progression of the texture.
For another example of a symmetrical chaconne structure,
see my listening guide for the 4th movement of Brahms' Symphony No. 4.
