I found a road atlas for £2 which had more than enough pages and were perfectly the right size. I found a few tutorials for scrapbook paper gift bags but I thought I would share my steps for a specific map print one as I found a couple of alternative methods that worked well for me and also the ease of the graph of the map for measuring.
I counted 7 squares from the tom and then folded in the base. I made a crease both ways on this.
Completed bags ready for the party!