info visualisation - How to indicate that part of a chart can be re-scaled or redefined visually to present a clearer, and/or more specific representation of the data?

I'm wondering about several issues I have with drill down behavior on graphs: How can we visibly show that a certain graph is "drillable" (affordance issue). In more details:

1. On a single chart, how to show that a certain graph type (column against line) is "drillable"? (a mouse click will allow to see the same data in a different dimension)


2. On a single chart, how to show that a certain point on a graph is "drillable"?


3. On a single chart, Drill down only for this month forward - there is a vertical line that indicates the current month and data shows both the past and the future. Drill down is possible only from this month.

Answer

A common and typical approach is cursor modification coupled with visual changes as the cursor moves over the item.

If you were to move the cursor over an item which would allow you to drill into, you could change the cursor accordingly, such as we do with a link. Couple this with a visual change to the foreground or other aesthetic modification and I believe the user will quickly grasp that the cursor and visual changes define an area where additional action can transpire.

Remember that all you need to convey is the initial affordance. The user will adapt to what a given area does based on the affordance over time.