Latin formation dancing is a team sport in which up to eight couples perform a coordinated choreography. A central part are the patterns formed by the dancers on the dance floor and the transitions between them. Planning and practicing patterns are some of the most challenging aspects of Latin formation dancing. Interactive visualization approaches can support instructors as well as dancers in tackling these challenges. We present a web-based visualization prototype that assists with the planning, training, and analysis of patterns. Its design was iteratively developed with the involvement of experienced formation instructors. The interface offers views of the dancers' positions and orientations, pattern transitions, poses, and analytical information like dance floor utilization and movement distances. In a first expert study with formation instructors, the prototype was well received.