There are two plots in this figure, one for the ADF data format and one for the HDF5 data format, both showing the file size in bytes vs the number of points per zone. Each plot has five curves, corresponding to results for 1, 10, 100, 1000, and 10000 zones.
For both data formats, the file size appears to vary linearly with the total number of points, at least for the two largest cases. For a total of 109 points (i.e., one zone with 109 points, or 10 zones with 108 points each, etc.), the file size is about 4 gigabytes. For a total of 108 points, the file size is about 0.4 gigabyte. The plot scale is such that relative differences can't be distinguished fot the three smaller cases, but for all three the file size is less than 0.1 gigabyte.