Knit in four quarters, beginning at each corner and ending in the middle. The quarters were attached as I knit the center sections, using a combination of sliding loop (learned from: http://string-or-nothing.com/2009/01/15/log-cabin-modular... and/or http://holliyeoh.com/sliding-loop-technique-photo-heavy/ ) and picking up an edge stitch to work together with the last stitch on the row. No sewing at all!!
Many balls of yarn were worked from both ends at once and weighed on an electronic scale to be sure I’d be able to match the mirroring unit.
This is the first Rambling Rows in which I actually had something approaching a plan before beginning!

I used the ‘crochet-hook cast-on’ for all cast-on edges.

I also made a chain selvedge by always slipping the first stitch knitwise and purling the last stitch of every row. That makes picking up stitches for the next unit infinitely easier. I only pick up in the back loop; that makes a neat twisty-looking line as a border between units. (I should get a close-up of that line!)

I used yarn from my unlisted stash - 100% acrylic, since I know how it will be (mis)treated! Who knew I had that many different shades of blue!! My sister asked for a blue afghan to match my nephew’s new bedroom; good thing she likes it! ;)