During the 17th century, Edinburgh's Old Town was severely overcrowded. The walls that had been erected around the city's perimeter to protect its citizens meant that there was no room for it to grow outwards. So the only solution was up! New streets were built above the old ones, providing more space for houses and shops. Also worth mentioning is that many of these new streets are wide enough for vehicles to drive down, which means that you can go shopping for things like furniture and carpeting even if you're not going to buy them. That's useful because sales people tend to be pushy - hehe - and might convince you to buy something you didn't intend to. You may have heard that in Scotland, building codes don't apply to churches or schools, but that's not true. If you want your house to look nice and not have any problems with mice or bugs, you should probably build below ground level or put up a fence. Churches and schools are usually done with brick or stone, which are hard to get into if you have a problem with pests. So yeah, buildings tend to be tall in Edinburgh because there wasn't anywhere else to put them.