Although direct evidence of civic planning is rare among Mesoamerican sites, such features offer great insight into past practices, intentions, and urban transformation. Using data from the transition to the Late Formative period (ca. 400–300 BC), I argue that direct evidence of urban planning is present in the monumental constructions of Yaxuná in Yucatán, Mexico. There, investigators detected a series of carefully rendered incised lines directly on Floor 6 of the E Group plaza. Along with the buildings' exposed surfaces, incised lines served as visual markers for placing rubble and dry-core fill into two categories: large dry-core stones and small compact fill. These visual distinctions informed the location of features built on top of this fill, including Floor 5 and a causeway spanning the plaza's central axis, distinguished from the white floor surface sascab (a durable product of pulverized limestone) by a red-orange color. The incised lines at Yaxuná grant insight into how ancient builders envisioned public works and then implemented and completed features in a step-by-step design process, which required precision and foresight.