Students' environmental awareness can be increased through mathematics instruction in the context of real-world environmental problems. Students can learn how to develop a mathematical concept as well as how to make decisions about the best solution to environmental issues through this learning. The purpose of this study is to develop a hypothetical learning trajectory (HLT) utilizing a realistic mathematical method oriented toward environmental problem-solving. The resulting HLT design is the product of the research conducted during the preliminary stages of Design Research. HLT is based on the findings of a literature review, a curriculum analysis, and a qualitative investigation of student learning issues. Additionally, this design will be used in the subsequent stage of Design Investigation research, which will result in the production of Local Instructional Theory. The findings of this study reveal that the resulting HLT incorporates various student activities centered on environmental concerns for students to comprehend the concepts of point and line position in the Cartesian Coordinate System materials. This article provides a complete explanation of the HLT design, which includes the learning objectives, conjectures, or assumptions conducted by the researchers, as well as the learning activities.