The game Worldle (https://worldle.teuteuf.fr/) is related to the recent craze in online once-a-day puzzles like Wordle. You are shown the outline of a country and get six guesses. For each wrong guess, you are told the distance and direction to go to get to the right answer.
It is of course fun for lovers of geography. But it also presents an opportunity to attune to the relationship between coastline shape (or border shapes in general) and geographic region or other country characteristics.
For example, when I saw the Worldle for this country last February 26, I noticed the jagged coastline, and surmised that it might be of volcanic origin - a big clue given some general knowledge of the locations of the plates. (I wanted an illustrative example, but for those who want to play it from the link above, I'll refrain from spoiling it further by giving the full answer.)
I imagine that there may be other hints that can be derived from the coastline shapes or numbers of islands that would be correlated with the differences between islands in different regions of the earth. For example, if I see an atoll-like shape, I dare say it is more likely to be a Pacific island than something in the Caribbean, and having a closer first guess helps.
I'm guessing generic geographic knowledge can also be helpful for internal borders which are related to rivers and mountains, but I don't know much about general shape-related differences between such things in different regions.
To pose my question broadly: what other geographic and earth-science knowledge can you explain here or provide references to which would be both fun to study, and provide helpful background for playing Worldle?