The base was a great graphic of downtown Chicago from the in-flight magazine.
I cropped the image and resized it, then printed it out onto a sheet of perforated, ready to mail postcards from USPS.
I then worked on the next layer - a scanned-in set of cards for things I didn't do when I was there. Thought about doing them, but ultimately didn't.
Since the downtown graphic was bright and colorful, I set the layer to black and white, and removed some sections. Then sent the postcard sheet through the printer a second time for the black and white layer. This gives a different result than just creating the image digitally and printing once. This is the result - 4 postcard-sized sections.
I also created a second set, using 'things I opened in Chicago' as the black and white layer.
I played with the colors of the downtown graphic for the second set.