Although Web-based instruction provides learners with sufficient resources for self-paced learning, previous studies have confirmed that browsing navigation-oriented Web sites possibly hampers users' comprehension of information. Web sites designed as "categories of materials" for navigation demand more cognitive effort from users to orient their navigation behavior according to the Web site's structure. This study designs a GIS-interface Web site for students to experiment with exploratory learning. Learners interact with maps to retrieve related information and actively organize what they read to develop their own cognitive models. This research uses an exploratory learning Web site and a structured learning Web site to compare learners' comprehension of the content and behavior when browsing the Web site in an experimental design. The results show that learners using the exploratory learning Web site performed better in content interpretation than learners exposed to the structured Web site when employing diverse strategies. (Contains 4 figures and 2 tables.)