Some of us favor digitizing all or most of our source documents. But the subject came up: how can you get a complete image of oversized documents, such as maps, plats, etc? I managed to solve that problem with Adobe Elements® (OEM version) which came installed on my computer (did I mention I love cheap or “included” software?) If you use different photo-editing software, take a look at how it may work similarly to the following solution.
To create an image of an oversized document, I place as much of it as I can on my scanner, starting with a corner. I scan that portion of the document to a JPG format then I move the document around, making sure that there is some overlap between scans. Each scan creates a JPG “puzzle piece.”
Once I have created all the puzzle pieces, I bring them into Elements® and use the “photomerge” feature to combine them into a single image. Elements® examines the edges of each smaller image to fit it together, just like a puzzle. The feature works remarkably well. Only occasionally do I have to manually manipulate the combining of images to get the unified image that I want. Once I have a single image, I convert the unified JPG to a PDF file or leave it as a JPG. I personally prefer the PDF as it is a consistent format with all my other documents. But if the image is, indeed, a photo, I leave it as a JPG.
Your photo-editing software may not use the term, “photomerge.” It may go by another term, such as “landscape” or “panorama.”