How to make a solid grow within a map's boundaries

[take2visualmedia]

I have a map of the US that is over a background layer and I need to make a color "grow" or expand within a section of it but I can not figure out how to make it expand within the boundaries of the map image. Right now I am generating a circle that expands over the section but I am having no luck figuring it out. Thanks in advance.

 

[Hawk Teflon]

Layer>New>Solid
Turn it off, and create a mask around what you want that color.
Move 2 seconds in, keyframe mask position
Move to first frame, and make the mask points all meet in the middle of that area.
Keyframe Opacity from 0 (at 0 seconds), to 50 (at 2 seconds).

That should do it.

 

[handsome pete]

You can also duplicate the layer with the borders and use that as a track matte.