Map and Table Calculation

ISUNDEF( ) function

Tests whether a is undefined or not known.

Syntax

ISUNDEF(a)

Input

a is the test condition: a boolean expression containing at least one map name or one column name

Output

ISUNDEF returns: if a is undefined, True is returned;

if a is not undefined, False is returned.

Domain: system domain Bool

Notes:

Tips:

Usable in

MapCalc, TabCalc

Examples

MapCalc example using a value map:

Below, the ISUNDEF function is combined with a conditional IFF function.

OutMap = IFF(ISUNDEF(DEM),1000,DEM)

DEM

OutMap

300 ? 400
? 100 ?
500 200 600
300 1000 400
1000 100 1000
500 200 600

Note:

Expressions OutMap = IFUNDEF(DEM,1000) or OutMap = IFUNDEF(DEM,1000,DEM) give the same results.

MapCalc example using a class map:

OutMap = IFF(ISUNDEF(Landuse),"Mountains",Landuse)

 

Landuse

OutMap

? F G
L L ?
G ? F
M F G
L L M
G M F

In OutMap, class name "Mountains" (i.e. M) is assigned for every undefined pixel in map Landuse. To all other pixels, the original class name is assigned (F=Forest, G=Grassland, L=Lake).

Note:

Expressions OutMap = IFUNDEF (Landuse,"Mountains") or OutMap = IFUNDEF(Landuse,"Mountains",Landuse) give the same results.

TabCalc examples:

OutCol1 = ISUNDEF(Population)

OutCol2 = IFF(ISUNDEF(Population),0,Population)

OutCol3 = IFF(ISUNDEF(Landuse),"Mountains",Landuse)

 

Sitenr

Population

Landuse

OutCol1

OutCol2

OutCol3

1

850

Crops

False

850

Crops

2

?

Grassland

True

0

Grassland

3

600

Urban area

False

600

Urban area

4

950

?

False

950

Mountains

5

1250

Crops

False

1250

Crops

6

450

?

False

450

Mountains

7

?

Grassland

True

0

Grassland

8

900

Urban area

False

900

Urban area

 

See also:

IFUNDEF
IFNOTUNDEF
IFF
Map and Table Calculation : Assigning undefined values
How to calculate with undefineds in maps and tables