Glossary for Geospatial Science

extrema points:  The highest and lowest points and flat areas locally as indicated by the elevation raster cell values.  Extrema are change points determined by the comparison of each cell to the eight adjacent cells.  A cell whose eight boundary cells are all lower than the cell is defined as a single local maximum.  A cell whose eight boundary cells are all higher than the cell is defined as a single local minimum.  Two or more adjacent cells with the same value whose boundary cells are all lower are defined as contiguous local maxima.  Two or more adjacent cells with the same value whose boundary cells are all higher are defined as contiguous local minima.  Two or more adjacent cells with the same value whose boundary cells also have the same value are defined as a flat area.