The picture produced by Marshall Mateer was the initial stimulus, but it was the work of Sergey Larenkov that helped my ideas crystallize.
This image of Leningrad/St. Petersburg showed me how the past could be used to highlight the present, how it is part of the present.
More of his work can be found at : http://sergey-larenkov.livejournal.com/ which inspired others to copy his work, me being just one example.
It is interesting to note that sites such as Google’s http://www.historypin.com/ would not have become so interesting.