Fields Add

Field Definitions - Edit definitions of feature properties and user defined fields

With this function you can modify the definitions of predefined status fields (feature properties or data fields) or define new ones.

Fields: The fields are sorted according to their type (data fields followed by properties for single points, multiple points, lines and polygons), but can be sorted in any order. For fields with the same name and type the order determines their priority when using the field name in calculations (see Field Name).

Move Up : Moves the active field one row up (increases priority of fields with the same name).

Move Down : Moves the active field one row down (decreases priority of fields with the same name).

Add (Taste Alt+A): Adds a new field with the current settings to the list after the current position (only possible if all parameters are filled in correctly and there is no other field with the same description). If there is already a field with the same field name and type, a warning is displayed.

Update (Taste Alt+U): Updates the settings of the active field (only possible if they have been altered, all parameters are filled in correctly and there is no other field with the same description). If you select another field without clicking on before, you will be asked if you want to update the previously modified field (), skip the changes () or continue to edit the field ().

Remove (Taste Alt+R): Deletes the active field from the list (confirm with ). If you want to delete a field that is used in the function of other fields, a warning is displayed. You should not delete those fields, but hide them (select Hidden at Status), otherwise you will obtain unexpected results and errors at the evaluation.

Description: This description must be unique for each field, because it is used to identify it and is displayed when the user has to select status fields in a dialog. The description can be chosen freely, but should be obvious and include the data type (Point, MultiPoint, Line or Polygon).

Field Name: This is the name of the field when it is created in a table actually (maximum 10 characters). This name [in square brackets] can be used as a variable in other functions too.

Note: You can define several fields with the same field name and data type but different functions and descriptions. You can select each version of this field in the selection list of the dialog (via its description). But if you use this field name in the functions of other fields, only the first definition is used (thus the order in Fields defines the priority of the different versions among each other).

Function: This is the avenue function, that is evaluated for the calculation of the field value (it must necessarily be adjusted to the data type - the method ReturnArea for instance is only valid for polygons). The syntax corresponds to the expression that must be typed in the Field Calculator (see ArcView Online Help theme Calculating field values, sub theme Performing operations on numeric fields), i.e. field names must be put in square brackets (e.g. [Area]).

If there is a status field of this name for the same data type, the calculation expression of this field is evaluated. Thus you can use other status field in the calculation expression, that don't have to exist in the table. If no field with this name and type is defined, the data table is searched for a corresponding field. If a field can't be found in a table too, a dialog window appears at evaluation time in which the user must enter the value of the missing parameter (see Update Fields).

If you use a undefined field name in the calculation expression, a warning is displayed. If you always want to use the field value of the table instead of the predefined status field, add blanks between field name and brackets (e.g. [ Area ]).

Please note that the following field names are internally predefined and should not be used:

[Shape]: The graphic feature (already projected when using a projection in the view - use [ Shape ] for the unprojected graphic object from the shapefile).
[Unit]: The unit in which the graphic feature is defined (Map Units of the view or projection).
[Rec]: The internal number of the record in the table (starting at 0).
[VTab]: The table object (the table that is updated).

Type: This setting defines the data type and thus the validity of the field (keep in mind that the Function must be adjusted to the data type und therefore the type of existing fields should not be changed):
- SinglePoint: Feature properties for single points.
- MultiPoint: Feature properties for multiple points.
- PolyLine: Feature properties for lines.
- Polygon: Feature properties for polygons.
- Data: User defined data field for any tables.

Status
: This setting defines the importance of the field.
- Default Field: These fields are created by default when using the option Create or Update Default Fields in Update Fields (and in all functions of the extension Arc4You Advanced Geoprocessing). Only the standard fields of ArcView Length, Perimeter and Area have this highest status.
- Normal: These fields are not created by default, but can be updated automatically (this is the status of most of the fields).
- NoAuto Update: These fields are not automatically updated when using the option Update Existing Fields in Update Fields. Use this status if there are fields with the same name in your tables that should not be updated by accident. Of course you can still choose these fields in the selection list of the dialogs and update their values if you like to.
- Hidden: These fields are excluded from the selection list and can therefore not be used and updated. Of course you can still use these fields in the calculation expression of other fields.

Note: You should better hide fields you don't need at the time instead of deleting them.

Specific Field Width: Normally all fields are created with the default width (16 characters with 3 decimal places). Activate this option if you want to set a specific width and accuracy for this field:
- Field Width: Total number of characters.
- Decimal Places: Number of decimal places (decimal accuracy).

Note: The decimal point itself consumes one place of the field width, i.e. the number of possible pre-decimal places results from the total field width minus the number of decimal places minus 1.

Default: Click on this button to load the standard definitions of the current field (see list below). If you confirm with the original definitions of all fields will be restored (Warning: In this case all changes of existing fields and all new defined fields will get lost).

Note: The changes of the field definitions will get lost if you uninstall the extension Arc4You Data. If you install the extension again, the standard definitions of all fields are available.

Click on to apply the changes of the field definitions and save them in the project permanently.

The following list shows all predefined status field and their calculation expression:

Field Name	Description	Function
*RecID*	Record number	[Rec]
Single Point
*XCoord*	X-coordinate of the point	[Shape].GetX
*YCoord*	Y-coordinate of the point	[Shape].GetY
MultiPoint
*Parts*	Number of single points	[Shape].Count
*Width*	Maximum width (distance)	[Shape].ReturnExtent.GetWidth Max [Shape].ReturnExtent.GetHeight
*Extent*	Area width (map units)	[Shape].ReturnExtent.ReturnArea
*Density*	Density measure (area representation of each single point)	[Extent]/[Parts]
PolyLine
*Length*	Line length in map units	[Shape].ReturnLength
*Parts*	Number of satially separated lines)	[Shape].CountParts
*Vertices*	Number of single points	[Shape].AsMultiPoint.Count
*Width*	Maximum width (distance)	[Shape].ReturnExtent.GetWidth Max [Shape].ReturnExtent.GetHeight
*Extent*	Area extension	[Shape].ReturnExtent.ReturnArea
*Distance*	Distance from startpoint to endpoint	[Shape].AsLine.ReturnLength
*Linearity*	Measure for linearity/curvature	[Length]/[Distance]
Polygon
*Area*	Area in map units	[Shape].ReturnArea
*Perimeter*	Perimeter in map units	[Shape].ReturnLength
*Acres*	Area in acres	Units.ConvertArea([Area],[Unit], #UNITS_LINEAR_YARDS)/4840
*Hectares*	Area in hectar	Units.ConvertArea([Area],[Unit], #UNITS_LINEAR_METERS)/10000
*Parts*	Number of partially separated areas	[Shape].Explode.Count
*Holes*	Number of real holes (islands)	[Shape].CountParts - [Parts]
*Vertices*	Number of single points	[Shape].AsMultiPoint.Count
*Width*	Maximum width (distance)	[Shape].ReturnExtent.GetWidth Max [Shape].ReturnExtent.GetHeight
*Extent*	Area extension	[Shape].ReturnExtent.ReturnArea
*Diameter*	Area diameter (approximate value)	[Shape].AsPolyLine.AsLine.ReturnLength
*Thinness*	Measure of thinness (see below)	[Width]*[Width]/[Area]
*Roughness*	Measure of rougness (see below))	[Perimeter]/[Area].Sqrt/4
*Convexity*	Measure of convexity (approximate value)	[Shape].ReturnBuffered([Width]*1.02).ReturnBuffered(-[Width]).ReturnArea/[Area]-0.15 Max 1
*Wideness*	Widest point (largest diameter)	av.Run("Lib.Shape.Center", {[Shape],0}).Get(1)
*Narrowness*	Narrowest point (smallest diameter)	av.Run("Lib.Shape.Narrow", {[Shape],0}).Get(1)
QDRatio *	Extension measure (reciprocal of Thinness* between 0 and 1=square)*	[Area]/[Width]/[Width]
Compactnes*	Measure for Compactness	[Area]/[Perimeter]/[Perimeter]
Circularity*	Circularity (measure for compactness between 0 and 1=circle)	[Area]/[Perimeter]/[Perimeter]Number.GetPi4
Unevenness*	Measure for unevenness (reciprocal of Circularity)	[Perimeter][Perimeter]/[Area]/Number.GetPi/4*
Convexness*	Measure for convexness (very slow but exact calculation)	av.Run("Lib.Shape.Hull",{[Shape],0}).ReturnArea/ [Area]

* These shape measures are very similar to others and are therefore not displayed (status Hidden).

Comments to some special functions:

Width: The width is the maximum extent in X-/Y-direction (e.g. 100 at an extent of 30/100 m) and is needed for other shape measures.

Thinness and Roughness: These two shape measures can be used for cleaning the polygon topology by detecting very small or frayed intersections or gaps (extension Arc4You Topology function Clean Polygons).

The Thinness of a polygon is the proportion between the square of its maximum extent and its area. It presents the reciprocal of the so called QDRatio or Thickness Ratio (which is for instance used at the extension Edit Tools from Ianko Tchoukanski). The larger the value, the thinner the polygon (at a value of 10 the polygon covers only 1/10 of its extent). Squares reach the minimum value 1.

The Roughness of a polygon is the proportion between its perimeter and the perimeter of a square of the same size and describes the frayness of the polygon outline. In opposite to the so called Sliver Ratio (ratio of area to extent) it is independent from the polygon size. The larger the value, the more frayed and ramified is the outline of the polygon (at a value of 10 the perimeter of the polygon would be 10 times longer as of a square). Squares reach the value 1, circles the minimum value of circa 0.7.

The thinness is in contrary to the roughness independent from the frayness of the polygon outline. A dense network of finest veinlets would achieve a large roughness, but a small thinness (if it covers most of its extent).

Wideness and Narrowness: The calculation of these two shape measures is done in separate scripts via numerous buffer operations and is very slow. The values represent the diameter of the largest circle, that can be placed inside of the polygon (or the smallest circle respectively that touches the outline at 2 diametrically opposite points). The narrowness can be used for cleaning the polygon topology by identifying bottleneck polygons (polygons with a constriction of a few meters or less probably should have been closed at this point and should be divided into 2 parts).