Geometry. This challenge is about the shapes and rhythms that make up the geometry of our world. Many photographs of any genre have an underlying sense of geometry, but I often like to make this the main subject of my work. I think it’s the most important aspect of a photograph’s success. This could be the patterns of the natural world up close and personal, or the rhythm of your local buildings. The above photograph, “Positive Negative,” depicts the Paula Rego Museum in Lisbon where the sky created an equally strong element of the composition as the building. The image has a totemic quality, softened by the passing cloud. I had waited for this cloud to move into the perfect position within the frame. The colour, light, and form of the image emphasize this geometry. by Cheri Lucas