In this reflective essay, Laurie H. Rubel, Maren Hall-Wieckert, and Vivian Y. Lim present a design heuristic for teaching mathematics for spatial justice (TMSpJ) based on their development of two curricular modules, one about the state lottery and the other about financial services in a city. Spatial tools, including data visualizations on maps and participatory mapping, were designed for youth to examine spatial injustices in these systems. The authors' findings report reflections about supporting students to "read and write the world with mathematics" (Freire & Macedo, 1987; Gutstein, 2003). These reflections inform an expanded design heuristic for TMSpJ.