In analytical models of salt diapirism, the initial salt-layer thickness and the post-deformation spacing of salt structures are key parameters. Here, 3D seismic data from The Netherlands offshore has enabled these parameters to be measured over large areas which can then be compared with model predictions. Estimates of the original salt-layer thickness were obtained by spatially filtering present thickness, using filters with varied spatial scales that remove local effects. Loss of evaporite minerals by dissolution or erosion during exposure, cannot be ruled out and, as such, thicknesses are minima. Spacing estimates were derived in two dimensions by locating the minimum separation of lines representing ridgelines of diapirs/walls. Because the length scale of spatial filtering was chosen based on the dependent variable, diapir spacing, the results are non-unique. Nevertheless, choosing an apparently optimal filter length of 50 km, a ratio between diapir spacing and original thickness from 12 to 20 is defined. This ratio is greater than has been reported for the pillow province of the UK North Sea Quadrant 44, which is as expected if pillows evolve into diapirs with progressive halokinetic deformation. This work is key to understanding the evolution of salt displacement, a necessity for unlocking remaining hydrocarbon resources.