By Harriet Baskas, msnbc.com contributor A popular way for visitors to get an overview of a city is from the observation deck of an iconic structure such as New York’s Empire State Building, Chicago’s Willis Tower (formerly the Sears Tower) or Seattle’s Space Needle, which joins the Seattle World’s Fair in celebrating its 50th anniversary on April 21. Created as the centerpiece of the 1962 space-themed exposition, the 605-foot-tall Space Needle has been described as looking like “a UFO on stilts” and was for many years the tallest building west of the Mississippi River. Today, the still futuristic-looking Needle is an iconic landmark in the Emerald City, its most visited…