def make_data(self):
        """Return data of the field in a format that can be converted to JSON
        
        Returns:
          data (dict): A dictionary of dictionaries, such that for a given x, y pair,
            data[x][y] = {"dx": dx, "dy": dy}. Note that this is transposed from the
            matrix representation in DX and DY
        """
        X, Y, DX, DY = self._calc_partials()
        data = {}
        import pdb
        for x in self.xrange:
            data[x] = {}
            for y in self.yrange:
                data[x][y] = {"dx": DX[y, x], "dy": DY[y, x]}
        return data