If you have a clear unobstructed view of the city, it will impact your market value. But this is a much less important feature than all of the regular real estate criteria~ condition, neighborhood, size, etc.
In a competitive situation where one unit has a view and one doesn't, all else considered being the same, the property with the view will sell for more. This will show up especially with condos in a larger complex. Most single family homes have enough differences that one or another feature will be more important in a value comparison than the view might seem to warrant. In this situation, the view's value will likely show up in making one property more competitive and sell more quickly than the one without the view. It may not gain you 10% more in selling price, but you may sell 50% more quickly than the competing property and that difference could easily be worth 10% in saved expenses!