I always take the opportunity to photograph cities from their designated lookouts. The view from the Latin American Tower in Mexico City is a must for any tourist. The city disappears into the haze in all directions but the tower is close enough to the historic center, known as Zocalo, on one side, and the high-rise towers on the other, for a good selection of shots.
Cities offer enormous photographic opportunities.
Within all cities you'll find focal points that present scenes, buildings and activity that typify the country and go way beyond the glossy brochures. After you've seen the famous places, spend some time wandering the streets, observe daily life and delve deeper into the city atmosphere. The key to photographing a city is to walk, walk, and walk. City tours are offered everywhere and are useful to get a quick overview of a new city and its main sights. However, they have limited use for good photography as they're usually run in the middle of the day and give very little time at each destination.