Frequently asked question

The Slope tool (within the Spatial Analyst extension or 3D Analyst extension) requires an immediate neighborhood (3 x 3 window) to calculate the rate of maximum change in z-value for the center cell. If any neighborhood cells are NoData, they are assigned the value of the center cell, then the slope is computed. For instance, a perimeter cell with a value of 4

, some cells within its 3 x 3 neighborhood are NoData, the Slope tool will assume them to be the same value as the center cell, which is 4 in this case

, then calculates the slope value.

However, the Slope function in a mosaic dataset does not assume pixel values. If any neighborhood cells are NoData, the center cell will be NoData in the output slope raster

.

Therefore, when running tools like Extract Values to Points on points located at these boundary pixels, a value of -9999 (NoData) may be received for slope values when the slope raster was created using the Slope Function, and instead get data values for the same boundary cells if the raster was created from the Slope tool.

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