Visualizations may help students understand the network of connections among multiple documents. This study explored how ninth-grade students used a novel digital document mapping scaffold to construct models of multiple documents. We examined students' maps and mapping processes in order to understand how they used the scaffold to visually represent multiple scientific documents on a controversial issue. We also investigated the relations between document mapping and argumentative writing in order to clarify how mapping might support written argumentation. Lastly, we explored how students perceived the purposes of document mapping. We found that students used the scaffold to construct several types of models that varied in their degree of source vs. content separation and integration. About half of the students constructed full documents models. Interleaving reading and mapping led to construction of more elaborate and well-integrated maps. Students who created more elaborate and two-sided maps also wrote essays that better integrated multiple documents in order to synthesize and weigh competing arguments. Students who revisited the maps and the documents while writing wrote essays that included and cited more documents. Students described document mapping as a tool for selecting and connecting sources and claims in order to support understanding and writing. These findings reveal how document mapping can support comprehension and integration of multiple documents. The findings also shed new light on how students construct documents models and on the relations between representations of multiple documents and argumentative writing. These results have implications for both theory and instruction.