Lucas,

I am using EasiSuites with Intellicalc.  Ted can probably explain it better than I can.  ES creates contours based on the legend applied to the map.  If you have 5 ranges in the legend, it will create 5 zones/ranges.  If you use a gradient legend, you can have infinite ranges.  The map pictured comes from the 2006 crop year.  It was created using 2005 yields.  I think I broke the yield into 20 ranges. but I am not certain on that.  The map is the actual application map.  There is only one rate per polygon.  The rate does not change inside the polygon.  But if you notice, the rates are not fixed based on the color.  For instance, I see one polygon on the right(east) with 441 #/ac.  Then there is another polgon to the lower left (Southwest) of the same color with a rate of 442 #/ac. 

In short, the rate does not change inside a polygon, but the range of rates is almost infinite.  I am not limited to 5 rates.

Again, I am not saying my method is the best or anything like that.  I am just laying it out as another option.  I hate to see fields cut up in square grids, but that is just a pet peeve of mine.  But I do like the appearance when I overlay my application maps on the yield data.