How to symbolize areas with unknown values

You can set individual cells of a raster surface to be transparent using the Layer Properties dialog box in ArcScene. This is particularly useful for rasters that contain cells with no measurement values. These cells are usually represented as NoData values or background values and can be rendered with a solid color. Displaying the NoData values and background values as transparent usually provides a better representation of the data and also reduces obscuring of underlying data. To set the No Data and background as transparent, use the no color option.

Steps:

1. Right-click the raster layer in the table of contents and click Properties.
2. Click the Symbology tab.
3. Check the box to Display Background Value.
4. Click the Background color selector drop-down arrow and click a color (or no color).
You can optionally define the raster's background color by checking Display Background Value and typing a value.
5. Click the Display NoData as color selector drop-down arrow and click a color (or no color).
A screenshot of the raster symbology settings for background and no data color.
6. Click OK.