This crochet afghan was created on the diagonal. While in-progress it grew larger and larger, becoming a seemingly immense triangle shaped half square, eventually levelling off to a tidy rectangle. The technique for this blanket is known as Corner to Corner or C2C. It's a simple easy pattern that is definitely worth a go, even for novice crocheters. There are several excellent video tutorials to be found online by searching "corner to corner crochet" and "C2C crochet."