We have clickable bubbles, and we also enable zoom-in for a selected area. What would be the best we to make the zoom-n capability understandable by the user? Should the cursor depict an arrow or something else?
You might consider letting the user know where they are, spatially speaking, using a navigator pane akin to that in Adobe Illustrator.
Note I've taken the zoom slider from this blog post from Gimp's UI team.
The benefit is that the user does not have to zoom back out to navigate to a different area.
Change to the 'Drag' cursor upon hovering over the active area in the navigator to let them know they can drag it.
This is at the expense of screen space however, and might conceal information underneath.
Show Click-ability with Hover States
Users will intuitively mouse over the objects. You should provide some feedback, in the form of a hover state (shown below as a circular highlight), when they do.
Show Zoom-ability with a Zoom Slider
The UI control that conventionally communicates "You can zoom in and out on this page" is the (usually vertical) slider, shown in the image below.
If it's also possible to zoom with a mouse or keyboard keys, you might consider showing a tooltip when the user interacts with the zoom slider, briefly explaining the other options.
Here's the image I stole the slider from, which I found by Google Image searching 'zoom slider control'.
What about changing the cursor into a magnifying glass? And of course, elements' feedback on hover... Always! :)