Bring your map into Vegas at as high a resolution as you can and then use the “Event Pan/Crop” tool to zoom in. It’s a “crop” button on the right side of the clip (event) on your timeline.

(Sorry, I’m in the middle of a render and can’t give you a better screenie.)
There are some tricks here:
* The crop tool will match your image dimensions/aspect and not your project. This is a good thing, because you can work with all of the extra resolution of your larger image however…
* The crop won’t match your project’s aspect, so you’ll get back bars top/bottom or sides until you match the crop to the project. I’d do this by first getting it roughly right and then using the numerical values in the dialog to get it perfect.
* You can also use the numerical values to enter the dimensions of your project first (say, 1280×720) and then click the Maintain Aspect Ratio button in the dialog to keep everything perfect as you resize. This is often how I “cheat”.
The Track level Track Motion tool will also work and is a more intuitive to use (in my opinion), but it only works at the project’s resolution, so when you zoom in, things may become pixelized, even if your map is a gigantic high-res image. This is why the Event Pan/Crop is a better tool to use.