Civilization 5 – How to Get Altitude Training for Units in Civilization 5

A lot of wonders (if not all of them?) show up as a visible model around the city in which they are constructing / constructed. So if you see a pyramid around a city, you know the the great pyramid is built there.

It takes some practice to know what wonder is what, and it's definitely a very crude way; requires scanning all cities for things that are sometimes very hard to notice. But it does work, I use this method often to know which wonder is being constructed by other civilizations, to avoid working on the same wonder.

Notice that all wonders have different "under construction" and "completed" models.

EDIT: I've found this wonderful page which attempts to catalog all wonders with screenshots of their "under construction" and "completed" models. Still incomplete, but useful nonetheless.

I would say that the only reason not to build on a hill is because there is a better spot. That might seem like dodging the question, but I guess the point is that while hills are good, they are not so good that there aren't plenty of situations where something else would be better. Maybe building off the hill gives you access to a resource you would otherwise miss. Maybe building on the hill keeps you away from the coast when you want to be able to build naval units. Or maybe you play a very Great Person heavy strategy and want to be by a river to build a Garden.

I almost always build my capital in the location that my settler starts, regardless of whether it is on a hill or not. Generally the starting location is dead center with a bunch of resources, and even that one turn of not building your capital does have a multiplied effect over time. So I would say that you should definitely take hills into account when planning city locations, as they are quite nice, but don't get so focused on them that you miss out on other locations that might be better.