Interiors are only loaded when you're inside them so even if you'd glitch under the map somehow you would see the infinite void. But if you enter the interior in a non-standard way (like teleport to it in SP) you will be able to zoom out the map and see where exactly the interior is. Since Further Adventures in Finance and Felony, Rockstar has been hiding interiors under Terminal, as - I assume - they've ran out of space under Legion Square/Mission Row and Terminal is less crowded. (If you