I've seen maps in print split across two pages. Occasionally they turned the map 90 degrees so it would fit on a single page. It's kind of hard to squeeze a detailed map onto a small piece of paper in a smaller-format book. To spread the image across two pages, you have to create two separate images, one for each side of the image. To do that, just open the image in a graphics editing program like Pixelmator or Photoshop and copy one half of the image into a new image and then the other half of the image into another new image. Each of these new images will go on facing pages to show the map split across two pages.
An ebook is a different matter. An ebook is essentially a web site. Each chapter of an ebook is an individual HTML page. As such, the text displayed behaves exactly the same way the text on a web page would behave in the web browser you use on your computer. This also includes how it will handle images placed inline. Grab the edge of this web browser window and shrink and grow the page back and forth. You'll see the text flow to match the new margins and the images jump to try and fit in the window.
This is why ebooks (and webpages) are referred to as flowable text.
While text can be stretched and cut fairly easily and automatically, images cannot. An image can be shrunk to fit on a page, but the programs running on ebook readers are not sophisticated enough to cut an image in half automatically. Just as in print, you will have to split the image. But ebooks only portray one page at a time, so the reader will only see one half of the map and then the other half. It might be wiser in this case to rotate the image 90 degrees so it can be displayed in its entirely on a single page. The reader can then hold the ebook reader sideways to study the map and, if the ebook reader has this function, expand to zoom in on a particular feature on the map.
Do NOT have any text elements on the same page with the map image. If the user decides to increase the font size, the letters will push the image to the next page. That would cause problems with your layout. If you absolutely must have words with the image, then edit the image to include the text in the image itself.
In theory, you could use SVG (Scalable Vector Graphics) to generate your image in an ebook. But the problem with that is the ebook reading devices do not handle SVG images in a consistent manner. In fact, they barely support it. I have successfully embedded SVG images into ebooks, but the results were less than satisfactory as different ebook readers rendered the image differently. SVG images hold a lot of promise for customizing the look of an ebook, but only if the manufacturers of ebook readers step in and clean up the code they use for handling SVG images.
