Surveys of the radionuclide content of land areas that may have been contaminated are required to determine whether there is an existing hazard to workers or the public. The objectives of this paper are to compare the results and uncertainties of in situ and ex situ measurements on land areas at a decommissioning nuclear site for the three different survey objectives, and to propose a new method for estimating the size and shape of in situ specimens that can be used to optimise the design of objective-driven in situ surveys.