The invention is a method using a computer to construct a grid representative of the distribution of a physical property of an underground formation having application to petroleum reservoir development. A set of initial grid cells MI containing at least one conditioning point PC is defined. Each cell MI is then visited and assigned a value representative of the property using a filling method. At least one unvisited cell (MNV1, MNV2) adjacent to at least one already visited cell MV is then identified, and the number N of adjacent cells MV is determined for each cell (MNV1, MNV2). Each cell (MNV1, MNV2) is then visited and filled according to the decreasing values of N. The stages of identification and filling of cells (MNV1, MNV2) are repeated until each cell of the grid has been visited.