I want to include a chart in my thesis to visualize an idea but the chart is not based on real data, it just helps me to explain a concept. How can I label it so it's not confused for actual data.
It is similar to this famous RUP hump chart which is also just educated guess of the author.
I've done this in a number of documents, where I state clearly that it is "illustrative" or "used to demonstrate a concept and the rough proportions of one item to another.
I've found I have the least amount of confusion by stating in the paragraph just before the chart appears, and then stating in the graph somehow.
I've seen this done with a "watermark" that says (usually) "sample data" (kind of like this, from here, though that's a table rather than a chart). Think of the "draft" watermark you sometimes see on documents; same idea. Saying something in the text (or figure caption) can be helpful, but this approach has the advantage of embedding the information directly in the graphic -- particularly useful if you're publishing online where somebody might save and reuse your image file, or if you're using the same chart in multiple sections of your document or multiple documents.
The graph will have a description with it. Just like every figure and table have. For example, Figure 5: Blah Blah Blah.
You can, after describing the entire graph, write in brackets something on the lines of "chart based on hypothetical data; for illustrative purposes only".
