Some pretty decent online maps here:

http://www.clickthai.de/Land/Karten/download.html

I wonder what paper size is required ?

Not too many details in the northern map on this site, really and enough roads missing to make a difference in a trip. They do have the main roads, which may be all that some people need. For a general idea of what is what and how far from one to another, it is a decent online map. I wouldn't bother downloading it for the 576 baht asking price. I do like the city to city kilometer chart provided on that site here: http://www.clickthai.../distanzen.html

For a good, detailed, folded paper map of northern Thailand, the GT-Rider Golden Triangle map is pretty good. Those are available all over Chiang Rai for 150 baht and include detailed city maps for northern area, tourist and historic sites and sleeping and eating establishments. They also come in a waterproof plastic version, 250 baht, but the paper version is nice because you can pencil in your own notes, dirt tracks, favorite sites, prices, dates and eating places.

I keep seeing some of the locals perusing a large atlas book-type map but I haven't seen it for sale or been able to get a good look at it and see just what all it offers.

large atlas book-type map

I forgot what's the scale but it is available at SE-ED

I use Map Magic. Fantastic map for the whole Kingdom. They also have one version for Bangkok and nearby provinces. Fantastic detail. There is a user interface where you can turn on/off icons on the map - e.g. if you want to have PTT petrol stations displayed - go to the Layer section and click on the PTT icon. Bought the CD at Se-Ed.

The Atlas is ::Thailand Deluxe Atlas, Bilingual maps in Thai and English. Cost is B 550 and should be available at any bookshop. Publisher is:Thinknet Co. Ltd..Phone :023526999, Email:onfo @thinknet.co.th..Second edition published 2007. It is excellent. beats any "folding" map hands down.

The Atlas is ::Thailand Deluxe Atlas, Bilingual maps in Thai and English. Cost is B 550 and should be available at any bookshop. Publisher is:Thinknet Co. Ltd..Phone :023526999, Email:onfo @thinknet.co.th..Second edition published 2007. It is excellent. beats any "folding" map hands down.

Thanks for that.