A CROSSTAB (Cross-tabulation) combines two grids into one resulting grid. Every possible combination of values is supported. If your source grids each have three classes, the possible combinations = 3 x 3, or 9 classes. The result of the crosstab will have a maximum of 9 classes.

In the example below two grids (GRID 1 and GRID 2) are set up for a CROSSTAB. The small grid in the centre is the CROSSTAB matrix. For example, when a cell labelled 'Spruce' from Grid 1 is combined with a cell 'Crown Land' from Grid 2, the result will be Index 4 .

Click on the 'Overlay' button to view the results for all cells. Examine the results and be sure you understand why the values were assigned.

Typically, a CROSSTAB produces far too many values to have much use in analysis. Two grids with 5 classes each would require up to 25 classes in the result. To avoid such a mess, a reclassification is normally required. A RECLASS reduces the number of classes to simplify and summarize results of a crosstab.

Here, you can perform a reclassification by clicking the 'Clear' button, then using the palette to assign your own values. Try using the following scenario:

I have the following forest harvest guidelines:

• I can cut on TFL or Crown Land
• Douglas Fir has a high value
• Spruce has a lesser value
• Red Cedar is not marketable

1. Don't Cut -- Red Cedar or Private Land
2. Low Value: -- Spruce and (Crown Land or TFL)
3. High Value -- Douglas Fir and (Crown Land or TFL)

Try setting this up and performing the overlay. It should end up looking something like: