Map calculation

Classifying maps according to a two-dimensional table

Two-dimensional tables are used to combine or reclassify two raster maps with a Class, Group or ID domain. It defines a new class or a value for each possible combination of input classes, groups or IDs.

A two-dimensional table view consists of rows representing one domain, and columns representing another domain. In the two-dimensional table, you have to assign a value, class name or ID to each possible combination of your input domains.

Application of a two-dimensional table on the command line of the Main window, requires two input raster maps which have the domains as used by the two-dimensional table. The output raster map then contains the values, classes or IDs that you entered in the fields of the two-dimensional table.

When you create a new two-dimensional table, it is directly displayed in a table window where you can also edit it directly. To open and edit an existing two-dimensional table, double-click a two-dimensional table in the Catalog, double-click the Open or Edit item in the Operation-list, or select the Edit Object command on the Edit menu of the Main window and select a two-dimensional table.

To apply a two-dimensional table:

A two-dimensional table can be applied by typing the following expression on the command line of the Main window:

OutMap = Two-DimTableName[InMap1,InMap2]

where:

OutMap	is the name of your output map.
Two-DimTableName	is the name of your two-dimensional table (extension .TA2).
InMap1 InMap2	are your input maps from which the domains are used in the two-dimensional table.

Example:

Two small raster maps will be combined to one output map according to a two-dimensional table. The domain of InMap1 contains the IDs: A, B, C, D and E; InMap2 has the classes: P, Q, R, and S.

The two-dimensional table may for instance look like:

TwoDim.ta2

	P	Q	R	S
A	Very Low	Very Low	Very Low	Very Low
B	Very Low	Low	Intermediately Low	Intermediate
C	Very Low	Intermediately Low	Intermediate	Intermediately High
D	Very Low	Intermediate	Intermediately High	High
E	Very Low	Intermediately High	High	Very High

To apply this table to InMap1 and InMap2 and obtain OutMap use the following formula:

OutMap = TwoDim[InMap1,InMap2]

InMap1

InMap2

OutMap

A	A	D
D	A	B
B	C	C

Q	P	S
P	Q	Q
R	R	T

VL	VL	H
VL	VL	L
IL	I	H

OutMap has pixel values according to the classification given in the two-dimensional table TwoDim. Each combination of corresponding pixel values is assigned its new value.