Datashader's approach is a bit different from an accumulation buffer, though similar in principle. It's not 3D rendering, and has no need for a z ordering; instead it's essentially 2D histogramming. For points, it simply takes each point, calculates which pixel it would land in, and aggregates per pixel, without ever storing all the data points per pixel. The key benefit over something like SciPy's histogram2d functions are in how it is implemented and used -- highly optimized, and highly integrated with viz tools so that it can let you just interact with your data naturally as if you had infinite resolution. Try it and see!