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According to http://en.wikipedia.org/wiki/Universal_Polar_Stereographic_coordinate_system. the area covering Arctic is less than Antarctic. Any reasons for it?

It is due to the shape of the lands?

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up vote 5 down vote accepted

The basic reason is that the UPS starts at 84 degrees North, and at 80 degrees South, but I guess you knew that. So lets look at why that might be. If you look at a map, there isn't a lot of landmass around 80 South. However 80 North does have a lot of landmass, so 84 North is a bit more useful to avoid changing from UTM to UPS.

Note that this the "common case" for maps, but it is not universal. DMA TECHNICAL MANUAL 8358.1 states that:

2-5.2.1 Maps at scales of 1:500,000 and larger for areas between 80° south and 84° north, and some hydrographic charts at 1:50,000 and larger, are based on the Transverse Mercator Projection.

2-5.2.2 Maps at 1:1,000,000 scale between 80° south and 84° north, some hydrographic charts, and aeronautical charts at 1:500,000 between 80° south and 80° north, are based on the Lambert Conformal Conic Projection.

2-5.2.3 Maps at 1:1,000,000 scale and larger of the polar regions (south of 80° south and north of 84° north), some hydrographic charts smaller than 1:50,000 and at latitude between 70° and the poles, and aeronautical charts at 1:500,000 north of 80° north or south of 80° south, are base, on the Polar Stereographic Projection.

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+1 Re your last remark: the spheroid is perfectly symmetrical about the equator, so the south will always have exactly the same shape and size (and therefore area) as the north when bounded by the same absolute latitude. –  whuber Feb 15 '13 at 16:18
    
@whuber: Can you explain this a bit further? I understood that the WGS-84 spheroid was not symmetrical about the equator (but was "fatter at the bottom"), and that the area bounded by any two (opposing) meridians would be slightly larger on the southern side of the equator. I'm always happy to learn something though, and I'd like to fix my answer to avoid any errors. –  BradHards Feb 15 '13 at 23:23
    
I don't know where you got that information--it's simply not true. Look up the parameters anywhere, such as on Wikipedia for instance. It's possible you are thinking of a gravitational datum, but those are not used in GIS. –  whuber Feb 16 '13 at 2:17
    
Perhaps I was thinking of the geoid. Fixed in any case. –  BradHards Feb 16 '13 at 23:27
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