Visualisation design requires critical thought: to understand important facets, investigate design suitability and explore alternatives. But, especially for learners, it can be difficult to structure a critical reflection of creative solutions. We introduce the Critical Design Survey (CDS): structured method that facilitates visualisation design analysis through reflective and critical thought. Applying the CDS helps someone to structure critical thought, provides a unified method that can be readily taught, learners can actively engage with the process and directly use it to write a critical-thinking report of their design ideas. The CDS contains three steps: Step 1, summarise and write down the essence of the idea. Step 2, perform an in-depth critique (we define 30 questions structured in six perspectives). Step 3, synthesise the ideas, implications, and decide on the next steps. We present the CDS, describe our design process (critical thinking workshops, talk aloud, and student use), and describe our use in teaching visualisation to undergraduate and postgraduate students.