I thought I'd try and add this to the map, for two reasons. Firstly the search couldn't 't find it and secondly it didn't appear on the map so it couldn't be seen. It was as if the Somerset Levels and Moors did not exist.
I thought I could improve upon this situation. The first challenge was to identify the boundary.
I couldn't find an official definition of the boundary but I locally the area is notable as a low-lying area of wetlands. The only thing that google turned up was several extremely low-res approximation maps. I was disappointed to find that every map was slightly different.
With no official definition of the boundary I had to devise my own set of rules that would trace the boundary.
Looking at some of the out-of-copyright 'historic' maps (available as a background in Potlatch) showed that the Somerset Levels and Moors are criss-crossed with drainage channels. If you follow these to the edges there is a 25 foot (or 10 meter on some maps) contour. I decided to use this contour as the boundary.
My next major stumbling block was finding that there is a limit of 4000 nodes per way. Drawing the entire area as a single way was out of the question. I eventually ended up with a lot of untagged ways all members of a single relation. I tagged the relation as a National_Park but it did not render. I changed the tagging to natual=moor but it also did not render. However after a couple of days it did appear in a search so that was one of my original problems solved.
To be continued...