Calculate Density

Calculate Density Tool The Calculate Density tool can calculate a magnitude-per-unit area from point features that fall within a neighborhood around each cell.

Workflow diagram

Calculate Density workflow diagram

Examples

  • Bird counts can be used to calculate species densities. The densities can then be compared to land-cover data to determine which habitats each species prefers.
  • The density of GPS measurements of flight paths can be calculated to determine which areas of airspace have high volumes of traffic.

Usage notes

  • The Calculate Density tool requires a single input of point features.
  • Input points are aggregated into bins for analysis. You must specify the Bin size to aggregate data into.
  • If you are aggregating into hexagons, the bin size d is the height of each hexagon, and the width of the resulting hexagon will be two times the height divided by the square root of three. If you are aggregating into squares, the bin size d is the height of the square, which is equal to the width.

    Hexagon and square height

  • You must specify a Radius that is greater than the bin size. The radius is used to find input features within the same neighborhood as the feature (bin) of interest.
  • There are two options to calculate density Weight; the Uniform option sums all the values within the neighborhood and divides them by the area. The Kernel option weights values in the neighborhood by distance from the feature of interest and applies a kernel function to fit a smooth tapered surface to each point.
  • Density can optionally be calculated using one or more count fields. A count field is a numerical field that specifies the number of incidents at each location. Features such as cities or highways can use a count field when calculating the density of population or lanes of traffic, respectively. If you specify a count field, the density will be calculated for the count field in addition to the density of points.
  • Calculate Density allows you to optionally analyze using time stepping. Each time slice is analyzed independent of features outside of the time step. To use time stepping, your input data must be time enabled and represent an instant in time. When time stepping is applied, output features will be time intervals represented by the fields StartTime and EndTime.
  • Only areas within the neighborhood of a bin containing points will be returned.
  • Calculate Density requires the data be in a projected coordinate system. If your data is in a geographic coordinate system, use the Project tool first project the data to a projected coordinate system.

Parameters

ParameterDescriptionData Type

Input lLayer

The point features for which density will be calculated.

Features

Weight

The weighting applied to the density function.

  • Uniform - A magnitude-per-area calculation where each bin is equally weighted. This is the default.
  • Kernel - A magnitude-per-area calculation with a smoothing algorithm applied (kernel) that weights bins closer to the points more heavily.

String

Bin Type

The bin shape used to create the regular bins. Choices are Square or Hexagon.

String

Bin Size

The distance interval that represents the bin size into which the input points will be analyzed.

String

Radius

The search radius applied to density calculations.

String

Output Units

The desired area units of the output density values.

String

Population Field(s) (optional)

One or more fields denoting population values for each feature. The population field is the count or quantity to be spread across the landscape to create a continuous surface.

Values in the population field must be numeric. By default, the density of the count of input points will always be calculated.

String

Interval (optional)

A value that specifies the duration of the time step. This option is only available if the input points are time enabled and represent an instant in time.

Time stepping can only be applied if time is enabled on the input. For more information on how time stepping works, see How time stepping works.

String

Repeat (optional)

A value specifying how often the time-step interval occurs. This options is only available if the input points are time enabled and represent an instant in time.

String

Alignment (optional)

A date specifying the reference time with which to align the time steps. The default is January 1, 1970, at 12:00 a.m. This option is only available if the input points are time enabled and represent an instant in time.

Int64

Output layer

The output layer will contain the following field(s) in place of the original fields.

Field NameDescriptionField Type

density_COUNT

The magnitude-per-unit area from point features that fall within a neighborhood around each cell.

If field(s) are specified in the Count Fields parameter, this field will not be generated.

Float64

density_SUM_<countField(s)Name>

The magnitude-per-unit area from point features that fall within a neighborhood around each cell for the count field.

This field will only be generated if field(s) are specified in the Count Fields parameter.

Float64

Considerations and limitations

Density can be calculated for point features only.