A skyline is the artificial horizon that a city’s overall structure creates. Skylines serve as a kind of fingerprint of a city, as no two skylines are alike. For this reason news and sports programs, television shows, and movies often display the skyline of a city to set location. The Sky Line of New York City was a new term in 1896, when it was the title of a color lithograph by Charles Graham for the color supplement of the New-York Journal.

Paul D. Spreiregen, FAIA, has called a skyline “a physical representation [of a city’s] facts of life … a potential work of art … its collective vista.”

http://en.wikipedia.org/wiki/Skyline