red harbor cranes, power line poles, wooden railroad ties, the diagonal lines in the road, and the cross walk across the rails. The counting of the ties leads to the idea of iteration in computer programming and, more generally, to discrete mathematics, the core of computer science. For iteration, we can use a programming language such as Python or C to encode the syntactical form of the iteration for a computer program. Other computer science related topics include a labeled directed graph that defines a semantic network. Such a network captures the objects in the photo as well as the relations among those objects. The semantic network is generally represented by a diagram with circles (concepts) and arrows (directed relations). There are additional indirect mathematical relations, including a differential equation that would define the motion of the train engine, with time as an independent variable. Connecting school subject to standards Exemplars of informal learning, such as a math walk, create opportunities for traditional education in school. Math walks can be a component in classroom pedagogy or in an after-school event. A key strategy is to create a mapping from what is learned on the walk to what is learned in school. This task is complicated due to geographic region, classification, and standards. A math walk can be situated as early as elementary school. The map to disciplinary subject area in US Math Education begins with the majority of states having adopted Common Core, which includes English Language and Mathematics. Within each state's standards, one must identify the grade level. A table in Common Core, titled "Mathematics Domains at Each Grade Level" summarizes the mapping of math subject to level. Once the mapping is known between object on the math walk and corresponding school subjects, this mapping should be included as part of the walk information. This linkage will assist both student and teacher. "Know your audience" is key to the successful educational delivery along a math walk. References External links Math Tours at MoMath Mathematical Lens (NSF) walkSTEM Finding Computing in Everyday Objects (TedX talk) Charles River Conservancy Math Trails Maths in the City Math Talk Math Trail at City Hall Mathematics education Environmental interpretation