Google Earth type-of-functionality (alternative)?

I work for a land planning firm.

- I have a map (aerial) of an area.
- I have several PNG files that depict various land planning principles (like, dashed lines over the roads, certain colors for certain building types, etc.)

I'd like to have an app, like Google Earth, that allows multi-touch (pan, tilt, zoom), that allows me to overlay these separate PNG files on top of the underlying aerial.

It'd be great if I could toggle the layers easily "on and off" OR change the opacity of individual layers.

Thoughts?

 

Because Google Earth (for the iPad) will not let users load their own images/layers (which the desktop version let's users do)...And I need a mobile solution.