The output values from the CutFill function are correct, however, the output is displayed incorrectly. The values from the Value field are being used rather than those from the Volume field. To demonstrate this, open the attribute table for the output raster and look at the Area value for the row with a Volume of 0 (a value of 0 here indicates the areas where the surface material did not change between the two surfaces). Select this row to highlight it on the display. Then find all the positive and negative Volume values in the attribute table (net loss and net gain, respectively), and highlight them. Notice that the locations that are highlighted in the display are different than what you would expect based on the legend.
This is a known issue with ArcGIS 8.2 and 8.3.
The output is being rendered using the Value field instead of the Volume field, even though the field used on the Symbology tab of the output layer states that it is using the Volume field.
Solution or Workaround
This is fixed in ArcGIS version 9.0.
In previous versions, change the field and class ranges of the values displayed in the legend.
- Right-click the layer in the table of contents and click Open Attribute Table.
- Right-click the Volume field and click Sort Ascending. Make a note of the last negative value before zero.
- Right-click the output layer and click Properties > Symbology tab.
- Select Volume for the field (even though it is already displaying Volume, reselect it).
- Click the Classify button. Use 3 classes and enter the correct break values. The first value will be the negative value just before zero that you noted, the next will be zero, and the last will be the highest value in the dataset.
Remember the following rules regarding the Classified renderer:
- The first value of the first range is inclusive, as is the last value of the first range.
- The first value of the second range is exclusive and the last value of the second range is inclusive.
- The first value of the third range is exclusive and the last value of the third range is inclusive.
For example, take the following classification ranges:
-100 -> -10 (inc -> inc) - first class range
-10 -> 0 (exc -> inc) - second class range
0 -> 100 (exc -> inc) - third class range
(inc = inclusive, exc = exclusive)
The value of -10 will be included in the first class range and not the second, because the last value of the first class range is inclusive to that range and the first value of the second class range is exclusive (not included in that range). The value of zero will be included in the second class range because the last value of the second class range is inclusive to that range. The first zero of the third class range will not be included in that range because it is exclusive to that range.
- Enter the labels for the legend items. Negative values will have a label of Net Gain, values of zero will be labeled Unchanged and positive values will be labeled Net Loss.