Here is a great project coming to you from Better Homes and Gardens Stitchery and Crafts 1966. In this project you are to use the techniques of crayon overlay, crayon scratchboard and crayon transfergraph.
They have used different drawing as cities as their examples. For the Tokyo picture they used the scratchboard technique. In this you sketch your design, re-draw them using India Ink and color them in with crayon. Then you apply a thin coat of paint or ink over the design and when it is dry scratch it off with a pointed tool.Rome was done with crayon transfergraph. To do this you apply colored chalk to a sheet of drawing paper. Then apply a layer of white wax crayon over the chalk. Then add another layer of wax crayon over the white layer. When this image is ready place a sheet of paper on it and use a hard pencil to redraw the picture on this new sheet of paper. This will transfer the color to the new sheet. How fun is that?
For Istanbul they used an overlay technique. First they painted their design with smooth tempera paint. then when the paint dries crayon is applied over all the areas. Once you are finished with the crayon you then scrape it off giving the image interesting texture.
Admittedly the article goes into more detail about the techniques and if you are interested in any of them let me know and I'll give you the whole shebang. It's kind of a cool craft idea though, one I found unexpected. Has anyone worked with crayon crafts before?