Figure 3

Privacy-preserving heat map and contour plots. Figures (A), (B) and (C) show the heat map (top rows) and contour (bottom rows) plots of X and Y from datasets D1, D2 and D3 respectively. From left to right we demonstrate the plots produced by: (i) the actual 30 by 30 density grid matrix; (ii) the actual 30 by 30 density grid matrix but suppressing any grids with density less than three counts; (iii) a generalized to 15 by 15 density grid matrix and suppressing any grids with density less than three counts; (iv) a 30 by 30 density grid matrix of deterministically anonymized variables using the value of \(k=3\) when locating the k-nearest neighbours; (v) a 30 by 30 density grid matrix of probabilistically anonymized variables generated by adding random noise to the actual variables, of variance equal to 6.25% of their actual variance. Note that the colour scale differs between the different heat map plots