A need for better ecology visualization tools is well documented, and development of these is underway, including our own NSF funded Visualization of Terrestrial and Aquatic Systems (VISTAS) project, now beginning its second of four years. VISTAS' goal is not only to devise visualizations that help ecologists in research and in communicating that research, but also to evaluate the visualizations and software. Thus, we ask "which visualizations work, for what purpose, and for which audiences," and our project involves equal participation of ecologists, computer scientists, and social scientists. We have begun to study visualization use by ecologists, assessed some existing software products, and implemented a prototype. This position paper reports how we apply social science methods in establishing context for VISTAS' evaluation and development. We describe our initial surveys of ecologists and ecology journals to determine current visualization use, outline our visualization evaluation strategies, and in conclusion pose questions critical to the evaluation, deployment, and adoption of VISTAS and VISTAS-like visualizations and software.