
Michael H. answered 03/14/19
Education Graduate from BYU in Social and Physical Sciences
One I've heard more recently is to picture a ladder standing up against a wall. The rungs of the ladder ("ladder" sounds like "latitude") run left to right. Climbing up the rungs means increasing your latitude, or climbing the ladder from one latitude to a higher latitude. Whereas the long side of the latter, which runs perpendicular to the rungs, goes up and down. The long side is the longitude line.
You could also visualize yourself saying each word. When you say the first syllable of the word "latitude," your cheeks spread apart from each other and your mouth opens wider horizontally. On the other hand, when you say the word "longitude," you open your mouth to form a taller and thinner "o" shape. Thus you could think of "latitude" as horizontal and "longitude" as vertical based on the shape your mouth makes when you say the words.