To create the colorful background, the students used bleeding tissue paper, applied to wet paper. I happened to have an overabundance of blue and pink tissue paper, so I encouraged them to mix the blues and add a little pink to suggest a morning or evening sky. They just needed to brush on a little water, apply a torn piece of tissue paper, and continue applying sections of tissue until about half the paper was covered. We let it sit for about a half hour, then peeled off the tissue paper.
I love the colors of the buildings drawn on maps, and it was interesting to watch kids actually choose sections of maps to use. One student even flipped her map over and drew a building on the list of cities. The skies are particularly beautiful. We had talked about leaving white space to represent clouds, and many did, but the best part of this was that no glue was involved at all... just water! The colors are brilliant and the blending is actually more interesting than with a tissue paper (with glue) collage because the water helped bleed the tissue color more fluidly than glue.
This lesson will definitely go into my file for future use... and I still have a ton of maps!