Bathymetry data from multibeam echosounders and other acoustic sources are now
widely available in the form of digital terrain models, which are conveniently displayed
as raster grids in desktop geographic information systems. Calculation of terrain vari-
ables such as slope is a simple push-button operation in most geographic information
systems; however, as we demonstrate here, there can be a great variation in the slope
values obtained due to computation algorithms and resolution or analysis scale. This
article also demonstrates how Monte Carlo simulation can be used to visualise uncer-
tainty in the underlying bathymetry dataset and also how this uncertainty impacts on
slope calculations.