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Field calculator

 
The Field Calculator is used for copying fields, concatenating (i.e., combining) strings, performing most mathematical calculations, and entering raw data. The Field Calculator can be used for conditional reclassification, complex mathematical calculations, and extracting geometric and geographic information.  The following section explains how to use the field calculator to add new data in the attribute table.
 
The Field Calculator is designed to assist the user in creating SQL expressions.  SQL is the acronym for Structured Query Language.  A syntax for retrieving and manipulating data from a relational database. SQL has become an industry standard query language in most relational database management systems.
 
The Field Calculator is used to construct SQL expressions to do calculations based on either the Geometry or the current attributes of the selected layer.  By using a combination of Fields, Operators and Functions, an SQL expression can be build to do a specific calculation.  It also allow the user to do general attribute management of the values in each field (e.g. to round a number or split text string in portions)
 
Please note: 
  • Data fusion results can only be added to a users own data layers and not on the MapAble spatial database. This is to ensure that the data from the various custodians in the MapAble database stay in it's original state.  The layers in the MapAble database can however be used for analysis purposes to add results to the users own data layers.
 
To access the Field Calculator,  the user can click on the field in the attribute table in the Table Mode.  Once the user clicked on the dropdown arrow of the field title, the following dropdown box will appear from which the user can select the field calculator:
 
 
The Field calculator dialog box which opens up, is structured in the following way:
 
Field calculator
1

Attribute fields

1. Attribute fields
 
The attribute fields is a list of all the current fields in the selected layer's attribute table.  Calculations can be done based on one or more of these fields if required.
2

Expression display

2. Expression display
The Expression Display shows the user how his expression is developed as he/she goes along constructing it.
3

Arithmetic Operators

3. Arithmetic Operators
 
Arithmetic Operators are used to specify conditions in an SQL statement and to serve as conjunctions for multiple conditions in a statement.
4

Functions

4. Functions
 
SQL has many built-in functions for performing calculations on data.  More details on SQL expressions and on each function in MapAble can be studied by going to the SQL Function FAQ section
5

Clear Expression Box

5. Clear Expression Box
The Clear expression menu item lets the user clear the Expression Box and start over again
6

Expression text block

6. Expression text block
The Expression Box is the same than the Expression Display but also lets the user edit the expression at any time during construction.
7

On screen numerical values

7. On screen numerical values
The on-screen numerical values lets the user use the mouse to select values as an alternative to the keyboard.
8

Expression Validation

8. Expression Validation
In order to check if an expression is correctly constructed, the user can click on the Validate button to test the expression and establish the correctness thereof.