Sum Attributes - Summarize field values of source theme (aggregated spatial join)

With this function you can perform aggregated calculations for several records, i.e. transfer attributes from a source theme to several destination themes by joining the themes spatially (according to the spatial relationship of their features) and by summarizing the field values of all overlapping features (sum, minimum, maximum, majority, standard deviation etc.). 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 considered with this function. The calculations can be made without priority, weighted by the degree of overlap or reduced proportionally (i.e. the largest area or the longest way inside of the polygon or the nearest situated point have the highest weight). 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).

The order in which these fields are added can be changed with the following buttons:

Note: The name of the created fields consists of the first 3 letters of the function name followed by an underscore and the name of the source field (e.g. Min_Area for the minimum value of the field Area, only Minority is abbreviated with Mnr). If the created field names became too long and were truncated, they can be changed with Rename Fields using the alias "A" afterwards.

Warning: The correct choice of the calculation method is crucial for the correctness or the results. Check your data before each calculation carefully though. If you want to calculate fields that depend on areas and fields that are independent, you have to perform the calculation in two separated steps.

Weighting factor: The field values can be weighted or reduced 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:

© 2003 WLM Klosterhuber & Partner OEG