Available with Spatial Analyst license.
Summary
Calculates a magnitude-per-unit area from polyline features that fall within a radius around each cell.
Illustration
Usage
Only the portion of a line within the neighborhood is considered when calculating the density. If no lines fall within the neighborhood at a particular cell, that cell is assigned NoData.
Larger values of the radius parameter produce a more generalized density raster. Smaller values produce a raster that shows more detail.
The values on the output raster will always be floating point.
The Output cell size can be defined by a numeric value or obtained from an existing raster dataset. If the cell size hasn’t been explicitly specified as the parameter value, it is derived from the Cell Size environment if it has been specified. If the parameter cell size or the environment cell size have not been specified, but the Snap Raster environment has been set, the cell size of the snap raster is used. If nothing is specified, the cell size is calculated from the shorter of the width or height of the extent divided by 250, in which the extent is in the Output Coordinate System specified in the environment.
If the cell size is specified using a numeric value, the tool will use it directly for the output raster.
If the cell size is specified using a raster dataset, the parameter will show the path of the raster dataset instead of the cell size value. The cell size of that raster dataset will be used directly in the analysis, provided the spatial reference of the dataset is the same as the output spatial reference. If the spatial reference of the dataset is different than the output spatial reference, it will be projected based on the selected Cell Size Projection Method.
For data formats that support Null values, such as file geodatabase feature classes, a Null value will be ignored when used as input.
If the area unit scale factor units are small relative to the features (length of line sections), the output values may be small. To obtain larger values, use the area unit scale factor for larger units (for example, square kilometers versus square meters).
See Analysis environments and Spatial Analyst for additional details on the geoprocessing environments that apply to this tool.
Syntax
LineDensity(in_polyline_features, population_field, {cell_size}, {search_radius}, {area_unit_scale_factor})| Parameter | Explanation | Data Type |
in_polyline_features | The input line features for which to calculate the density. | Feature Layer |
population_field | Numeric field denoting population values (the number of times the line should be counted) for each polyline. Values in the population field can be integer or floating point. The options and default behaviors for the field are listed below.
| Field |
cell_size (Optional) | The cell size of the output raster that will be created. This parameter can be defined by a numeric value or obtained from an existing raster dataset. If the cell size hasn't been explicitly specified as the parameter value, the environment cell size value will be used if specified; otherwise, additional rules will be used to calculate it from the other inputs. See the usage section for more detail. | Analysis Cell Size |
search_radius (Optional) | The search radius within which to calculate density. Units are based on the linear unit of the projection of the output spatial reference. For example, if the units are meters—to include all features within a one-mile neighborhood—set the search radius equal to 1609.344 (1 mile = 1609.344 meters). The default is the shortest of the width or height of the output extent in the output spatial reference, divided by 30. | Double |
area_unit_scale_factor (Optional) | The area units of the output density values. A default unit is selected based on the linear unit of the output spatial reference. You can change this to the appropriate unit if you want to convert the density output. Values for line density convert the units of both length and area. If no output spatial reference is specified, the output spatial reference will be the same as the input feature class. The default output density units are determined by the linear units of the output spatial reference as follows. If the output linear units are meters, the output area density units will be set to Square kilometers, outputting square kilometers for point features or kilometers per square kilometers for polyline features. If the output linear units are feet, the output area density units will be set to Square miles. If the output units is anything other than feet or meters, the output area density units will be set to Square map units. That is, the output density units will be the square of the linear units of the output spatial reference. For example, if the output linear units are centimeters, the output area density units will be Square map units, which will result in square centimeters. If the output linear units are kilometers, the output area density units will be Square map units, which will result in square kilometers. The available options and their corresponding output density units are the following:
| String |
Return Value
| Name | Explanation | Data Type |
| out_raster | The output line density raster. It is always a floating point raster. | Raster |
Code sample
This example calculates a density raster on a length field of a polyline shape file.
import arcpy
from arcpy import env
from arcpy.sa import *
env.workspace = "C:/sapyexamples/data"
outLDens = LineDensity("roads.shp", "LENGTH", 45, 1000, "SQUARE_MILES")
outLDens.save("C:/sapyexamples/output/ldensout")This example calculates a density raster on a length field of a polyline shape file.
# Name: LineDensity_Ex_02.py
# Description: Calculates a magnitude per unit area from polyline features
# that fall within a radius around each cell.
# Requirements: Spatial Analyst Extension
# Import system modules
import arcpy
from arcpy import env
from arcpy.sa import *
# Set environment settings
env.workspace = "C:/sapyexamples/data"
# Set local variables
inPolylineFeatures = "roads.shp"
populationField = "length"
cellSize = 120
searchRadius = 1500
# Execute LineDensity
outLineDensity = LineDensity(inPolylineFeatures, populationField, cellSize,
searchRadius, "SQUARE_MILES")
# Save the output
outLineDensity.save("C:/sapyexamples/output/linedensity")Environments
Licensing information
- Basic: Requires Spatial Analyst
- Standard: Requires Spatial Analyst
- Advanced: Requires Spatial Analyst