There are different perspectives in the literature on the examination of visual images used in course books. In this study, illustrations from the visuals used in geometry in the lower learning area of school mathematics were examined and summarized first by researchers and then by teachers and students. For many students, the mathematics coursebook is the first material they encounter in understanding the course content and conveying the mathematics culture. In this study, the illustrations related to the concept of Angle used in mathematics coursebook, two books published abroad, two books published in Turkey, for 5th-grade students were analyzed. The type of research is Document Analysis and the illustrations were examined in qualitative and quantitative terms. In this way, the study aimed to analyze the contribution of illustrations in mathematics education to the conceptualization of geometrical definitions through the coursebook and the contribution and effect of improving geometrical thinking. The results of the study showed that illustrations for the field of mathematics that is in coursebooks must include an algebraic representation.