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POP Data in Raster Mode

POP data that have 2D lat/lon coordinates can be plotted directly in physical space. Raster images of grids of this type are different from other raster grids in that we want the raster cell to be defined by its boundaries since there may be cells that are not perfect squares. The default raster behavior is to place the value in the center of a square.
poprast_1.ncl: The trick to tell NCL to create raster plots based on cell boundaries, is to have one more element in the coordinate arrays than the corresponding dimension in the data array.

Note that for the pop grid, ULONG and ULAT represent the cell boundaries. These are the arrays that need to be used.
poprast_2.ncl: Demonstrates a zoom plot.