[oasisbob]

> 100th parallel/the Mississippi.

Small point, but longitudinal lines aren't typically called parallels because they're not parallel to each other.

[dredmorbius]

More specifically: there are parallels of lattitude and meridians of longitude.

https://www.differencebetween.com/difference-between-paralle...

Meridian from "of the noon time, midday":

https://www.etymonline.com/word/meridian

As a mnemonic, the lines of longitude are all equally long (running from pole to pole).