I would like to make a projection of a field along 'z' axis centered at [0.5, 0.5, 0.5] with a thickness of 10Mpc (5 Mpc to +z dir and 5 Mpc to -z dir). 

How to select the above-mentioned region from the whole simulation volume?

I am using YT Legacy 2.x. 

Thank you.   
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