What is there that appears and disappears?
Julia looked at Thom with a very serious expression. Thom had a ready answer.
Anything in the city appears and disappears, anything changes all the time. Buildings are built, modified, submerged, emerged again, built upon, demolished and rebuilt all the time. The space between buildings changes shape all the time. I have a better question for you, what is there that does not change all the time?
helobiae 
For those of us looking for a constant in our lives, look no farther. Change is the only constant. I love your art!
Thanks!