Pitney Bowes MapInfo Vertical Mapper User Manual
Page 181
Chapter 10: Aggregating Data
User Guide
179
performed regardless of whether the dialog box is greyed out. If you do not choose any of the
settings in this dialog box, the default values will be used. A reminder will appear when this
technique is chosen.
Exploring the Select Aggregation Technique and Statistics Dialog Box
The Select Aggregation Technique and Statistics dialog box enables you to set the aggregation
technique and aggregate point attributes.
The Aggregation Technique section—enables you to choose one of the three aggregation
techniques: forward stepping, cluster density, and square cell.
The Aggregate Point Attributes section—enables you to choose the following statistical
parameters, computed during the aggregation process, that will be assigned to the aggregated point
file and region file (if chosen).
•
Minimum Original Value: The minimum value selected for aggregation.
•
Average of Original Value: The average value of all the points selected for aggregation. This
value must always be assigned to the new aggregated tables.
•
Maximum Original Value: The maximum value selected for aggregation.
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Median Original Value: The median value is the middle value of all points selected for
aggregation. If there is an even number of points, the median value is the average of the two
middle values.
•
Average of Min & Max Value: This value is the average of the minimum and the maximum
values.
•
Sum of Original Values: The value obtained by summing all values selected for aggregation.
•
Expected IDW Value: The value is obtained by summing the weighted value for each point
selected for aggregation and dividing this value-weighted sum by the sum of the weights.
The weight associated with each value is inversely proportional to the square of the normalized
distance between the value and the reference location. The normalized distance is the actual
distance from the reference point divided by 1.01 times the “same point” distance. Therefore,
values close to the reference point will have more influence than values farther from the
reference point. The inverse distance weighted value is considered to be a reasonable estimate
of the value at the aggregated coordinate.