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# DensityCalculator

Determines the density of a group of Candidate features.

Density is a measurement of Candidate values per unit area. It is calculated as a numeric value; the greater the value, the more dense are the Candidate features.

The density equation is Total Candidates/Area of Interest.

Total Candidates is defined by either:

• The total NUMBER of Candidate features
• The sum LENGTH of Candidate features
• The sum Area of Candidate features

Area of Interest is defined by the size of the first polygon feature that enters the Area input port.

## Caution

It’s VERY important to note that ALL Candidate features count towards the density calculation, even if they fall outside the Area feature.

In other words, this transformer does not test whether or not candidate objects are inside the Area feature. If you wish to use only Candidate features that lie within, or overlap, the Area feature, you should pre-process the data using either a SpatialFilter or SpatialRelator transformer.

## Usage Notes

• The geometry type of Candidate features may be points, lines, or polygons. However, Area features must be polygons.
• If excess Area features are supplied – i.e. there is more than one Area feature for a particular group – then they are excluded from the calculation of density for Candidates. However, they will still receive their own density calculation. In other words, each Area receives the density of Candidate features for their own size; but Candidate features only receive their density in relation to the size of the first Area feature.
• If you need to find the density of Candidate features against the total area of a number of polygon features, use an Aggregator to aggregate the polygons and input the resulting aggregate to the Area port of this transformer.

## Example

There are many possible uses for this transformer, including:

Density of disease (number of incidences per km2)

Density of traffic network (amount of road length per km2)

Density of land use (amount of industrial zoning per km2)

In this example, the density of cycle route network is calculated for a particular zipcode (postal code).

Area of zipcode: 195355642.75 ft2

Total length of cycle route: 83017.28 ft

Density: 0.000425

In this example, the cycle routes spatially overlap with the zipcode boundaries, and are clipped to match, but the DensityCalculator does not necessarily need this to be so.

If there were multiple zipcode features to be processed, then a group-by could be used in the DensityCalculator, using the zipcode attribute as the attribute to group-by. The result would be a count of the cycle route density for each zipcode.

## Editing Transformer Parameters

Using a set of menu options, transformer parameters can be assigned by referencing other elements in the workspace. More advanced functions, such as an advanced editor and an arithmetic editor, are also available in some transformers. To access a menu of these options, click beside the applicable parameter. For more information, see Transformer Parameter Menu Options.

## FME Licensing Level

FME Professional edition and above