I'm studying digital logic at university currently, and the textbook has an example of a 4 variable K-map drawn with the $x_1$ and $x_2$ on top. However, most places I can find draw the map inverted with the $x_1$ and $x_2$ on bottom. I've taken to drawing it that way also, only because it's faster for me to check my answers using other tools which all represent K-maps in this same way. The only difference seems to be that the book has minterms drawn in column major order, and the rest of the world has them drawn in row major order. Is there a correct or preferred way to draw a K-Map?
It's all up to you; different ways of drawing (four-variable) Karnaugh maps only differ in how variables are ordered. They all give the same results.