The resolution stays the same for me when I zoom in - the blocks just get bigger, but don't resolve to anything smaller making it look hugely pixellated. :(
By squares, I mean the square map areas, not individual blocks. I don't know if the map shows exactly the same for everyone but if it does; there are 4 black squares to the right of where I am right now, followed by a regular 'lit' square, followed by two 'shaded' squares.
The 'shaded' areas seem to be happening since Ant updated the plugins so there seems to have just been a change in how the map renders. So eventually the whole map should be more like that I think.
I have always assumed that the blocks on the map represent the chunks in the world, which could be 16x16
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everyone else: I came to find out about the grey shaded bits and you have no clue :(
maybe they are bits that have been explored but not visited recently?