tdrd, love the sketches. I should be so lucky to draw a straight line. The tutorial here, http://www.cadtutor.net/tutorials/bryce/keyframe-animation.php may be what you need to help do your zooming. I haven’t read the entire tutorial but it talks about Keyframes in Bryce. And, if possible, it may also be a way you can display different portions of your maps.
You maps would have to be made using a terrain, and modified using the Terrain Editor (TE). You could use the TE to modify a terrain or create a new one that suits your needs. There are tutorials at the above site and on You Tube that tell how to create, and modify, a terrain. Also, while in the TE you could create the path you want for the streams, rivers, or whatever you want then add a water plain and place it into your terrain so only that portion of water shows withing the stream paths created. It would mean you’d have to have a good elevation on your terrain map, or fairly deep stream paths, or you’d have water showing where no water should be.
The aerial maps I’ve seen aren’t very detailed unless you zoom in on them, so any vegetation, rocks, etc. wouldn’t have to be detailed but more a representation of what they’re suppose to look like. If, and I say if, keyframes works like I’ve seen in another program, you could zoom into any location by setting keyframs at each focal point until you actually got into the village, town, etc. Just before you entered the village, town, etc. you could blur the image and have the next image the actual village, town, etc.
I’m also guessing you know how to make, or import, the objects you’ll want in you images and on your maps. If you don’t know how any of this is done the above link, and You Tube, can help. Please keep in mind, I’ve never done Keyframes in Bryce, or watched any tutorials dealing with the subject, so it might be a good idea to look for tutorials at the above link and You Tube to see if it indeed will work for your project.