OK, let's get this straight. Map cases aren't the most exciting pieces of kit. Most are verging on useless - won't keep maps dry in anything but the lightest rain and start to crack within a few months. If you can't find a decent case laminated maps are one solution. If you do it yourself it has to be done very well if it's not going to crack and bubble after a couple of
years. Or you could let someone else do the hard work for you and buy laminated maps such as those from Aqua3 but they are rather bulky and cost about £12 a sheet - a lot of money for a map you may not use very often.
The document bags are the same basic design and come in sizes from A6 (just big enough for a wallet and a small mobile phone or a first aid kit) up to A3 (handy as an extra-large mapcase). They are just as waterproof as the mapcase. Prices start at about £6 for an A6 case (or £11.50 cheaper than a duplicate driving licence). Downsides? The mapcase only shows a couple of panels of OS map on each side (about 12km x 10km on a Landranger map). There's a little Ortlieb logo on one side that always seems to sit over something important. The plastic yellows over time and is quite tacky - the case doesn't slide into a Camelbak all that easily and squeezing a phone and a wallet into the A6 bag is hard work. All pretty minor. In short, if you expect to get a soaking this winter you'd be mad not to have a look at Ortlieb kit.
It's okay, I don't need a map to find my way to the Ortlieb wesbite.