Downsample 2D Elevation Map for Optimized Rendering 

Visualization of large datasets may require a lot of time and memory resources. Use resampling to decrease data dimensionality when a quick preview is needed.

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X data = Import["http://exampledata.wolfram.com/hailey.dem.gz", "Data"];

Compare rendering times for the original and resampled datasets with no or little discernible difference in the graphs.

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X {ta = First@AbsoluteTiming[gra = ReliefPlot[N@data]], tb = First@ AbsoluteTiming[ grb = ReliefPlot[ArrayResample[N@data, 240], ImageSize -> 240]]}

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X GraphicsRow[{gra, grb}]

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