As others have stated, country borders can be "fun". If I'm remembering R-Tree basically uses bounding boxes to help narrow down the candidates for you to do the more detailed check on. Consider for example that the Aleutian Islands in Alaska cross the 180th meridian. So the bounding box for the US is basically 360 degrees wide. So any point in the latitude range from the south of Hawaii to the north of Alaska will have the US show up as one of the possible countries to do a detailed check on. Depending on how detailed you need it you've also got multi-polys, holes, enclaves, whether the border ends at the ocean shore vs X nautical miles offshore, etc. And Lord help you if you're trying to do business in the countries with a border dispute. Country X will be rather harsh to you if you try to sell a product in their country that says area A is actually in country Y instead of being in country X like they claim it is. And likewise with country Y if you claim that A is in country X. But at least most of those are problems for the people making the map you're using, and not so much for you.