Rob's scatter plot shows four points positioned by x and y values, with each point colored red or blue based on a categorical "cat" field. The plot uses D3 v4's `d3.scaleLinear` to map data coordinates to SVG pixel positions and renders circles with `g.selectAll("circle").data(data)`. Axis labels and scales are generated through `d3.axisBottom` and `d3.axisLeft`. The data is hardcoded in the script, and the SVG canvas is sized at 250 by 250 pixels with fixed margins.