data = Flatten[Table[{x, y, x + y}, {x, 0, 10}, {y, 0, 10}], 1];
plot = Block[{data2, xmin, xmax, ymin, ymax},
   data2 =
    Reverse[Transpose[
      Partition[data[[All, 3]],
       Length[DeleteDuplicates[data[[All, 2]]]]]]];
   xmin = Min[data[[All, 1]]];
   xmax = Max[data[[All, 1]]];
   ymin = Min[data[[All, 2]]];
   ymax = Max[data[[All, 2]]];
   Show[ArrayPlot[data2,
     ColorFunction -> "M10DefaultDensityGradient",
     PlotRangePadding -> None,
     FrameTicks -> All,
     DataRange -> {{xmin, xmax}, {ymin, ymax}}],
    PlotRange -> {{xmin, xmax}, {ymin, ymax}}]];
Export["plot.pdf", plot]
Export["plot.png", plot, ImageResolution -> 500]