Labels in a zoomable interface

Question

I am working on a zoomable Sankey diagram hoping to be able to display small and big elements at the same time and I con not decide if labels should zoom or keep constant size.

Firstly the whole thing resembles a map, lets see what would Google do:

From perspective:

Zoomed to detail:

Zoomable Sankey with fixed size labels

I did something similar but I was told the in detailed zoom the labels looks lost, too small and disproportional inside larger element.

From perspective:

Zoomed to detail:

Zoomable Sankey with proportional labels

But if I zoom the labels too they are not readable from larger perspective at all.

From perspective:

Zoomed to detail:

What approach is more suitable for a diagram? Should I try to combine both approaches to overcome the shortfalls? Any ideas are welcome.

Please disregard other differences between the two models. To see any of the images in real size open it in new tab.

Answer 1

To me, the labels in both zoom levels of your original example look too small. It's possible that simply having a larger fixed label size will solve the problem.

If that isn't adequate, then you will have to do some kind of scaling, whereby the labels increase as you zoom in, but at a less than linear rate. This is do-able, but will be a bit tricky to get right.

Note: the Google example you show doesn't have fixed label sizes. They are slightly increased in the second map image. Appropriate labels with dynamic zooming are no easy thing to get right; Google and other mappers have put a lot of effort into this area.