doc:statistics

# Statistics

Documentation | Other Specifications | Statistics

The TatukGIS Developer Kernel statistics unit provides useful functionality relating to the computation of statistics from data contained by any type of geospatial layer.

The description of the DK's statistics unit can be found in this blog post and in the Delphi | .NET | Java | ActiveX class documentation.

Besides the computation of statistics from layer data, a key benefit of the implementation of the statistics is it offers the means to sometimes significantly speed up other processes, e.g., rendering, labeling, or classification.

#### Section rendering

A section can be defined using a query represented by formulas, e.g. render objects with a population greater than the median of all observations:

`POPULATION > MEDIAN(POPULATION)`

Virtual fields and complex queries are permitted

`(GIS_UID > MAX(GIS_UID) - 20) AND (AREA < AVG(AREA))`

#### Labeling

Label formatting described here can be extended using layer statistics with formulas, e.g.

• percentage of population rounded to one decimal place:
`{{(POPULATION / SUM(POPULATION)) * 100}:#.0} %`
• factor that determines the difference between an object's value to the minimum value of all observations, referenced to the range of values:
`{{(VAL - MIN(VAL)) / RANGE(VAL)}:#.00}`

#### Statistics functions

Almost all statistical functions from the `TGIS_StatisticalFunction` enum are available as query formulas:

• `COUNT` - responds to `TGIS_StatisticalFunction.Count`,
• `AVG` - responds to `TGIS_StatisticalFunction.Average`,
• `COUNTNULL` - responds to `TGIS_StatisticalFunction.CountMissings`,
• `MAX` - responds to `TGIS_StatisticalFunction.Max`,
• `MAJORITY` - responds to `TGIS_StatisticalFunction.Majority`,
• `MEDIAN` - responds to `TGIS_StatisticalFunction.Median`,
• `MIN` - responds to `TGIS_StatisticalFunction.Min`,
• `MINORITY` - responds to `TGIS_StatisticalFunction.Minority`,
• `RANGE` - responds to `TGIS_StatisticalFunction.Range`,
• `STDEV` - responds to `TGIS_StatisticalFunction.StandardDeviation`,
• `SUM` - responds to `TGIS_StatisticalFunction.Sum`,
• `VARIANCE` - responds to `TGIS_StatisticalFunction.Variance`,
• `VARIETY` - responds to `TGIS_StatisticalFunction.Variety`.
2019/09/27 13:23