Fields Add

Load Attributes - Load field values from source theme (multiple spatial join)

With this function you can transfer attributes of a source theme to one or several destination themes by joining the themes spatially (the field attributes of the source theme are added to the destination theme according to the spatial relationship of their features). This kind of join is only possible between the themes of the active view.

In opposite to the spatial join of ArcView (where only the field value of the first fitting record is used) the field values of all overlapping features are transferred to separate fields. The new fields are numbered consecutively (e.g. Area1, Area2, Area3 etc.) and the field values are sorted descending by the amount of overlap (e.g. the field values of the largest area or the longest line inside of a polygon are copied to the fields with index 1). This function is very powerful and of multipurpose use (see Examples of use below) and there are many differences to a normal spatial join (see Hints to join attributes).

You must activate the destination themes, to which you want to load attributes, before calling the function (click on them with the mouse pointer - keep the Shift key pressed to select multiple themes).

Source Theme: All polygon, line or point themes of the current view are listed. Select the source theme which attributes you want to add to the destination themes.

Source Fields: Select the fields of the source theme you want to transfer. The order in which these fields are added can be changed with the following buttons:
- Move Up : Moves the selected fields one row up. Keep the Ctrl key pressed to move the fields 5 rows up and the Shift key to move the fields to the top of the list.
- Move Down : Moves the selected fields one row down. Keep the Ctrl key pressed to move the fields 5 rows down and the Shift key to move the fields to the bottom of the list.

Additional Field Values: In addition to the loaded field values specific measures for the degree of overlap between the features can be created (e.g. OvlArea1, OvlArea2, OvlArea3 etc.):
- Overlap: Fields with the degree of overlap named OvlArea (intersection between polygons), OvlLen (length of the overlapping lines) or OvlDist (distance to the point).
- Relative Percentage: Fields named OvlRel with the relative percentage of overlap among the overlapping source features (sums always up to 100, independently from the size of the overlap between source and destination feature).
- Absolute Percentage: Fields named OvlAbs with the absolute percentage of overlap between source and destination feature (sums only up to 100 if the destination feature was completely overlapped). This fields is only created when the intersection between the features gives polygons, i.e. when the source and the destination theme is type of polygon (or the destination theme is buffered).

Clear Missing Numeric Fields: Activate this option if the field values of numeric fields, for which no overlapping features were found, shall be empty (otherwise they get the value 0).

Add Fields for Amount of Overlap: Activate this option to create the two fields OvlCnt with the number of overlapping features and OvlSum with the sum of the overlapping area, line length or point distance (sum of OvlArea, OvlLen or OvlDist). If the Absolute Percentage of the overlap is calculated, the field OvlPart is created additionally. This fields contains the percentage of the total overlap of the destination feature (sum of OvlAbs for all overlapping features).

Index Number of First Field: You can enter the index number of the first loaded field. At the default value 0 the first field won't get an index and the next fields start with 1 (e.g. Area, Area1, Area2 etc.). Use this option if you want to load attributes with the same name from several source themes to one destination theme. You can thereby define a different index range for each theme.

Maximum Number of Fields: You can define the maximum number of fields that are loaded per attribute. At the default value 1 only the field value with the largest overlap is loaded (this isn't always equivalent to the majority value - see function Sum Attributes). If you increase this number, field values with less overlap are loaded too (if that many features are overlapping).

Warning: Mind that dBASE tables are limited to a maximum of 255 fields. If you load 20 attributes, you can thus create only 12 fields per attribute. If your destination table already has numerous fields, this number decreases further and the function may be stopped with an error message.

Buffer Destination Features: Joining some theme types is only reasonable when the destination theme is buffered (i.e. points or lines are converted to buffer polygons before they are intersected with the source features). Lines can normally only be joined with those points that are situated exactly on the line or with those lines that share an identical line section. You also have to create buffer polygons when joining points to points. In all cases those source features are loaded that are situated within the buffer distance, all features that are more remote are ignored.

Click on

to run the function. Now all features of the source theme are intersected with those of the destination themes and the selected attributes are loaded, sorted by the degree of overlap. This may take some time with large data sets, especially if the features of the destination themes are buffered.

The status bar finally shows the number of loaded attributes and the number of destination records where several or no overlapping features could be found (and thus several or no field values could be loaded).

Weighting factor: The field values are sorted by the degree of overlap. The calculation of this factor and how the features are related and intersected, depends on the type of the source and destination theme ("buffer" stands for a destination theme of any type that is buffered during calculation):

Source	Destination	Condition for overlap	Weighting factor
Point	Point	coordinate is identically	record number
Point	Line	point is exactly on the line	position along the line
Point	Polygon	point is inside of the polygon	distance to the outline of the polygon
Point	Buffer	point is within the buffer	distance to the outline of the buffer
Line	Point	line contains the point exactly	position along the line
Line	Line	lines are overlapping	length of identical line section
Line	Polygon	line is intersecting the polygon	length of line section within polygon
Line	Buffer	line is intersecting the buffer	length of line section within buffer
Polygon	Point	polygon contains the point	distance to outline of the polygon
Polygon	Line	polygon contains part of the line	length of line section within polygon
Polygon	Polygon	polygons are overlapping	area overlapping with polygon
Polygon	Buffer	polygon overlaps the buffer	area overlapping with buffer
Polygon	=Source	polygons are adjacent	length of the common border line

Adjacent polygons without overlap are normally not considered. If a polygon theme is joined with itself though (destination theme identical to source theme), the adjacent polygons are included and the length of the common border line is used as weighting factor. Polygons that are only connected at a single point are still ignored. Buffer the features to include those neighbors too.

Examples of use:

Determine for each municipality the kind and length of all roads that run through it.
Determine for each plot of land the numbers and areas of all adjacent plots.
Determine for each forest area the kind of utilization of all other forest areas within a radius of 100 meters.
Determine for each forest area the numbers, areas and proportions of all plots of land.
Determine for each river the distance of the houses and the house numbers within a radius of 500 meters.
Determine for each spring the landuse within a radius of 1000 meters.
Determine for each house the traffic density and distance to the next main road.
Load for each polygon the attributes of the point that is closest to its center (i.e. has the greatest distance to the outline). This may be necessary if the topology of a polygon theme has been heavily altered and the attributes of old label points shall be taken over as good as possible.
Load for each line the attributes of those lines that are most similar (i.e. which buffer area has the longest intersecting line segment). This may be necessary if a new road network was digitized and the attributes shall be taken over from the old network as good as possible. This kind of attributing works best if the source theme was buffered before as well.
Load for each polygon the attributes of the polygon that is the most similar (i.e. has the largest overlap). This may be necessary if a polygon theme is available in different scales and the attributes shall be transferred from on to the other as good as possible.