While the tool parameters are important, striking a balance between the inputs and desired outputs can also be checked
We are doing this as to not use up space in our personal drives when experimenting with different radiuses. Enter the values above for the various parameters Keep the default location of Output Raster. This brings up the Kernel Density window. Similarly, to have the density units of your output in miles per square mile, set the area units to SQUARE_MILE.The kernel density GP tool calculates a magnitude per unit area from point or polyline features using a kernel function to fit a smoothly tapered surface to each point or polyline. In ArcToolbox, select Spatial Analyst Tools Density Kernel Density. To set the density to be in meters per square meter (instead of the default of kilometers per square kilometer), set the area units to SQUARE_METERS. You can control the density units by manually selecting the appropriate factor. The end result, comparing an area scale factor of meters to kilometers, will be the density values being different by a multiplier of 1,000. For example, if the linear unit is meters, the output area units will default to SQUARE_KILOMETERS and the resulting line density units will convert to kilometers per square kilometer. When an output Area units factor is specified, it converts the units of both length and area. The contribution of the line segment to density is equal to the value of the kernel surface at the raster cell center.īy default, a unit is selected based on the linear unit of the projection definition of the input polyline feature data or as otherwise specified in the output coordinate system environment setting. The illustration above shows a line segment and the kernel surface fitted over it. This results in a more generalized output raster.Ī line segment and the kernel surface fitted over it. The main effect of a larger radius is that density is calculated considering a larger number of points, which can be farther from the raster cell. Although more points will fall inside the larger neighborhood, this number will be divided by a larger area when calculating density. Increasing the radius will not greatly change the calculated density values. Under Spatial Analyst -> Kernel Density The kernel function is based on the quadratic kernel function. Comparing a unit scale factor of meters to kilometers will result in the values being different by a multiplier of 1,000,000 (1,000 meters x 1,000 meters). Point Density in ArcMap Distance0.3 Distance3. If an area unit is selected, the calculated density for the cell is multiplied by the appropriate factor before it is written to the output raster.įor example, if the input units are meters, the output area units will default to square kilometers. The values can be integer or floating point.īy default, a unit is selected based on the linear unit of the projection definition of the input point feature data or as otherwise specified in the output coordinate system environment setting. For example, a value of 3 would cause the point to be counted as three points. If a population field setting other than NONE is used, each item's value determines the number of times to count the point. The kernel function is based on the quadratic kernel function described in Silverman (1986, p. The density at each output raster cell is calculated by adding the values of all the kernel surfaces where they overlay the raster cell center. The volume under the surface equals the Population field value for the point, or 1 if NONE is specified. Only a circular neighborhood is possible. The surface value is highest at the location of the point and diminishes with increasing distance from the point, reaching zero at the Search radius distance from the point. Kernel Density calculates the density of point features around each output raster cell.Ĭonceptually, a smoothly curved surface is fitted over each point.