After seeing someone using Merkaartor to edit in OSM, I decided to give it a try last night. Before this, I've been exclusively using Potlatch. Potlatch is a pretty good application and is definitely the best Flash application I've ever seen but I quickly ran into one of its limitations while I was doing Eastwood City and Bonifacio High Street (in Metro Manila, Philippines). The limitation is that at the highest zoom level, you cannot place nodes more accurately: the nodes snap to a 3-pixel "grid". This 3-pixel grid translates to a resolution of almost 3 feet at the latitude I'm working at. This is more than good enough for roads, but not adequate for buildings. (I'm kinda OC ["obsessive-compulsive", slang in Philippine English] when mapping the details of buildings, and this limitation prevented me from making nice right angles of small idented corners of buildings. See this view of Bonifacio High Street for an example of non-perpendicular corners. I find this lack of right angles maddening! :-P) I asked Richard, Potlatch's creator, about it and he acknowledged this limitation (our conversation is at the OSM Wiki).

If you're using Potlatch, then Merkaartor gets some getting used to with regards to its interface. The workflow is pretty much the same as in JOSM: you go to an area, download the data, edit at will, then upload the changes. I like it because it doesn't have the aforementioned 3-pixel limitation, and in addition, it blows up the Yahoo! map tiles if they're not available in a higher zoom level; Potlatch just shows Yahoo!'s "We're sorry, the data you have requested is unavailable" tiles. (I'm not sure if Merkaartor's behavior is allowed by Yahoo!'s TOS).

I'll still continue to use Potlatch as a general editing tool since it's pretty quick and I'm used to it. I'll just bring out Merkaartor if ever I want some finely wrought detail. :-)

(This is also cross-posted, with some changes, to the talk-ph mailing list.)