Cities can be seen as the extended version of a house, also representing your emotional landscape but at a broader level.
If you're seeing it from afar, especially if you're currently living in the country-side, you may be ambitious. If you're entering it, you may have reached or will reach your goals.
The larger the city and the more hectic, the more you may be wishing for greater sociability in your life. It may also a sign for lack of peace and quiet in your current life.
If you're already living in a city, dreaming of one may indicate good business.