A few years ago a book won a prestigious award. It was the story of a woman who escaped from captivity and rescued her child by walking over the border between two countries. Unfortunately neither the author nor the editor did their homework. Those two countries do not share a border. It’s incredible none of the judges noticed that important detail either. But oh, wow, did the readers ever notice! The press caught onto the story and the award was withdrawn.
There is no excuse for such an error. Even if your internet is down and Google Maps won’t load on the internet café computers there are atlases and maps aplenty at the local library.
Far more common are errors in a story when the hero travels south to meet Grandma, then travels south again to take her home. Unless they both live at the North Pole, that isn’t possible.
Or it takes ten minutes to drive to work in chapter two and twenty minutes in chapter ten. If there’s a traffic jam the author needs to mention the fact.
I clearly remember reading a book where the name of the local town was spelled three different ways. A simple “find and replace” would have been an appropriate tool for that author to use.
Geography is particularly important when an author is creating a new world. How many suns and moons are there? What colors are they? Where are the hills? Lakes? Coastline? Towns? One author I know draws incredibly detailed maps. If cartography isn’t your thing, at least keep a spreadsheet with the information so you maintain consistency. Even if you think you can remember it all now, by the time you come to write a sequel you’ll find it invaluable.
And if you’re using real countries, please check out a decent map of them before submitting your book to an editor/agent/publisher. Being a laughing stock on Twitter is not good for your writing career.