=SİNK AND FİLL= A Sink is a cell with an undefined drainage direction; no cells surrounding it are lower. The pour point is the boundary cell with the lowest elevation for the contributing area of a sink. If the sink were filled with water, this is the point where water would pour out The z-limit specifies the maximum depth of a sink that will be filled. The z-limit is not the maximum depth to which a sink will be filled. All sinks that are less than the z-limit lower than their lowest adjacent neighbor will be filled to the height of their pour points. The number of sinks found with the z-limit will determine the length of processing time. The more sinks, the longer the processing time. The sink tool can be used to find the number of sinks and help identify their depth. Knowing the depth of the sinks can help in determining an appropriate z-limit for Fill. Fill can also be used to remove peaks. A peak is a cell where no adjacent cells are higher. To remove peaks, the input surface raster must be inverted. This can be performed with the Minus tool. Specify the highest value of the input surface raster as the input raster. How sink works? A sink is a cell or set of spatially connected cells whose flow direction can not be assigned one of the eight valid values in a flow direction raster. This can occur when all neighboring cells are higher than the processing cell or when two cells flow into each other, creating a two-cell loop. Sinks are considered to have undefined flow directions and are assigned a value that is the sum of thie posibble directions. How fill works? Sinks (and peaks) are often errors due to the resolution of the data or rounding of elevations to the nearest integer value. Sinks should be filled to ensure proper delineations of basins and streams. If the sinks are not filled a derived drainage network may be discontinuous. The Fill tool uses the equivalents of several tools, such as Local Flow, Flow Direction, Sink, Watershed and Zonal Fill, to locate and fill sinks. The tool iterates until all sinks within the specified z-limit are filled. As sinks are filled, others can be created at the boundaries of the filled areas, which are removed in the next iteration. The tool can also be used to remove peaks, which are spurious cells with elevation greater than would be expected given the trend of the surrounding surface.