It looks like patience is key for rendering the map. If I zoom in one a non-rendered area, it takes about 20 seconds to render. I don't know a whole lot about minecraft internals at this point, but I'm curious how the map rendering works. Does it poke the server and ask it to render new chunks in the area you've zoomed in on? Outside of the pre-fab area of these maps it's all procedurally generated, right?
Does this mean rendering areas of the map that haven't been rendered by the server already is a fairly expensive/slow operation for the server?
BTW, thanks for the quick response.