Calculate Density

Calculate Density diagram

This task creates a density layer from point features by spreading known quantities of some phenomenon (represented as attributes of the points) across the raster. The result is a layer of areas classified from least dense to most dense.

For point input, each point should represent the location of some event or incident, and the result layer represents a count of the incident per unit area. A higher density value in a new location means that there are more points near that location. In many cases, the result layer can be interpreted as a risk surface for future events. For example, if the input points represent locations of lightning strikes, the result layer can be interpreted as a risk surface for future lightning strikes.

Other use cases of this tool include the following:

Request URL

http://<raster analysis url>/CalculateDensity/submitJob

Request Parameters

Following is the list of parameters with syntax and details for each.

Parameter

Description

inputPointOrLineFeatures

(Required)

The feature layer that the density will be calculated on.

It can be a point, line or polygon dataset.

Syntax: This parameter can be:

  • a URL to an feature service layer with an optional filter to select specific features,
  • a feature collection.

Examples:

  • {"url": <feature service layer url>, "filter": <where clause>}
  • "inputPointOrLineFeatures":{"layerDefinition": {}, "featureSet": {}, "filter": <where clause>}

outputName

(Required)

This is the output image service name that will be created.

Syntax: A JSON object describes the name of the output or the output raster.

You can specify the name or you create an empty service using Portal Admin Sharing API and use the return JSON object as input to this parameter.

Output name example:

"outputName":{"serviceProperties":{"name":"testrasteranalysis"}}

Output raster example:

"outputName":{"itemId": <portal item id>}
"outputName":{"url": <image service url}
"outputName":{"serviceProperties":{"name":"testrasteranalysis","serviceUrl":"http://<server name>/server/rest/services/Hosted/testrasteranalysis/ImageServer"}, "itemProperties":{"itemId":"8cfbd3ec25584d0d8f4ed23b8ff7c43b","folderId":"sdfwerfbd3ec25584d0d8f4"}}

countField

Provide a field specifying the number of incidents at each location. If each point represents a single incident, do not provide a count field.

Domain: Integer or float field

Syntax: A string that represents a field name.

Example:

  • "countField": "myCountField"

searchDistance

The size of the neighborhood within which to calculate the density. The radius size must be larger than the binSize.

For example, if you provide a search distance of 1800 meters, the density of any location in the output layer is calculated based on features that are within 1800 meters of the location. Any location that does not have any incidents within 1800 meters will receive a density value of zero.

If no distance is provided, a default will be calculated that is based on the locations of the input features and the values in the count field (if a count field is provided).

Domain: Meters, Kilometers, Feet, Miles

Example:

  • "searchDistance": {"distance":"60","units":"Meters"}

outputAreaUnits

The desired output units of the density values.

The default is based on the units specified in your profile. If the units are set to Metric, the default is SQUARE_KILOMETERS. If your profile is set to US Standard, the default is SQUARE_MILES.

Possible area units are:

  • SQUARE_KILOMETERS
  • SQUARE_MILES

Example:

  • {"outputAreaUnits" : "SQUARE_KILOMETERS"}

outputCellSize

Specify the cell size to use for the output raster.

Domain: Meters, Kilometers, Feet, Miles

Default: Same as the analysis environment

Example:

  • "outputCellSize": {"distance":"60","units":"Meters"}

context

Context contains additional settings that affect task execution.

For this tool, there are five settings.

  • Extent (extent) — a bounding box that defines the analysis area. Only those areas in the inputZoneLayer that intersect the bounding box will have the statistics calculated.
  • Output Spatial Reference (outSR) — the output raster will be projected into the output spatial reference.
  • Snap Raster (snapRaster) — the output raster will have its cells aligned with the specified snap raster.
  • Cell Size (cellSize) — the output raster will have the resolution specified by cell size
  • Mask (mask) — only cells that fall within the analysis mask will be considered in the operation.

f

The response format. The default response format is html.

Values: html | json

Response

When you submit a request, the task assigns a unique job ID for the transaction.

Syntax:

{
"jobId": "<unique job identifier>",
"jobStatus": "<job status>"
}

After the initial request is submitted you can use the jobId to periodically check the status of the job and messages as described in the topic Checking job status. Once the job has successfully completed, you use the jobId to retrive the results. To track the status, you can make a request of the following form:

http://<raster analysis url>/CalculateDensity/jobs/<jobId>

Accessing results

When the status of the job request is esriJobSucceeded, you can access the results of the analysis by making a request of the following form:

http://<raster analysis url>/jobs/<jobId>/results/outputRaster?token=<your token>&f=json

Parameter

Description

outputRaster

This is the density raster.

Example:

{"url": 
"http://<raster analysis url>/CalculateDensity/jobs/<jobId>/results/outputRaster"}

The result has properties for parameter name, data type, and value. The contents of value is always the output raster dataset's itemid and the image service URL. For example:

{
    "paramName": "outRaster",
    "dataType": "GPString",
    "value": {
        "itemId": "f121390b85ef419790479fc75b493efd", 
        "url": "https://<server name>/arcgis/rest/services/Hosted/<service name>/ImageServer"
    } 
}

Related topics

7/5/2017