Why Is A Nautical Mile Longer Than A Regular Mile?

A land mile is a set distance, whereas a nautical mile will vary slightly in length depending on how close you are to the equator. This is all to do with the way the the earth can be seperated into degrees, but because it's not perfectly round, by the time you get to the outer edge near the poles the disatnce between is greater than the distance near the equator.
it's hard to explain but if you draw an orb on the page and draw lines going from the middle out, all at the same degrees in the middle you will see that as you go further north the distance becomes larger. Each of these degrees is then divided into forty (I think, but it's been a while since I did this) and these are nautical miles, therfore at the poles a nautical mile is longer than at the eqautor. It is hard to explain without drwaing a picture but I hope you've followed my gist!
If you ever look at a sailing chart you will see this is taking into account as variability. Peace

A nautical mile (symbol nmi) is the angular distance of one minute (1/60 degree) of latitude on the earth surface. The distance varies with the difference of latitude by its original definition. Now the internation conference has fixed its defintion as exactly 1852 meters.
 
The statute mile (symbol mi) is an unit of distance as measured on land. One statute mile is 5280 feet or 1760 yards, which is about 1,609 metres.
 
Why Is A Nautical Mile Longer Than A Regular Mile? It's by their definitions.  

Nautical Mile stands for a unit of length used in navigation; exactly 1,852 meters; historically based on the distance spanned by one minute of arc in latitude

where as .. A regular mile is a unit of length equal to 1,760 yards or 5,280 feet; exactly 1609.344 meters