Threshold areas are rings or drive times around a site that contain a specified amount of a variable. For example, you can create a ring around a site that contains 50,000 people or a drive time that contains 100,000 households. The threshold areas analysis starts from the site locations you specify and then expands outward until your threshold is met, creating rings or drive-time areas on the map. The resulting areas are stored in your project's content panel under Threshold areas (sites). You can export the results to Excel, run reports, or run infographics for the threshold areas.
You can create threshold areas for a single location, a point layer, or existing site locations. To use a point layer in the analysis, you can first add web maps or layers, import a file containing your locations of interest, or save a layer through points of interest search.
To create threshold areas, do the following:
- In the Maps tab, click Run analysis and then select Threshold areas.
The Threshold areas workflow pane appears.
- Click Get started. Optionally, check the Skip this in the future check box to bypass the Get started panel the next time you perform the workflow.
- Select Single location, Point layer, or Existing site(s) and then click Next.
- Depending on which option you select, complete the following steps:
- For Single location, enter an address, latitude and longitude values, or place a pin on the map to choose a starting location. Click Next.
- For Point layer, select a layer from the current project in the Choose layer window. If you selected a point layer containing more than ten sites, select a maximum of ten sites in the next panel. Optionally, pan and zoom the map to the area you are interested in and select Filter by map extent to view only sites in this area. Click Next.
Tip:
You can filter a layer by attributes in the project content panel and then use the filtered layer in the workflow. - For Existing site(s), select at least one site or up to ten sites in the Add sites window and then click Apply.
- Choose a variable for the analysis. Click Change variable > Browse for a variable to select a variable from the data browser.
- Define the thresholds for your analysis. Enter a numeric value in the Threshold 1 field and, optionally, in the Threshold 2 and Threshold 3 fields.
You can create up to three threshold areas for each location.
- Choose the type of areas to create. Select Rings or Drive time and then use the Units drop-down menu to choose units of measurement.
Rings can be measured in miles or kilometers, and drive times can be measured in minutes, miles, or kilometers. For drive times, your site locations must be within 12.42 miles (20 kilometers) of a street network.
- Optionally, click Threshold settings
.
Move the handle on the slider to run the calculation for better
performance or better precision.Optionally, in the Threshold settings pane, click More options to specify the target percent difference and increment size used when calculating the area. There are default values in these fields for each point on the slider. You can specify your own values or click Reset to return to the defaults. For more information, see Usage notes and Considerations.
Target percent difference—This parameter defines how much of the specified threshold value the area should contain. For example, setting a target difference of 5 percent means that the area should contain 95 percent of the specified threshold value. The target percent difference can be any integer between 1 and 10.
- Increment size—This parameter defines how far the area expands or contracts when the analysis checks the specified threshold value. For example, setting an increment size of 0.25 minutes means that the area will keep expanding another 0.25 minutes' drive time (15 seconds) until it reaches a threshold value within the target percent difference. The increment size can be any value between 0.01 and 5.
- Optionally, for Drive time, click More options to specify the following:
- Use the drop-down menu to choose a travel mode: Driving time, Rural driving time, or Trucking time.
- Choose a travel direction: Away from facility or Toward facility.
- Check the Use traffic check box. Choose Live traffic to calculate time based on current traffic conditions and use the slider to factor live traffic conditions up to 12 hours from the current time. Choose Traffic based on typical conditions for to set a day of the week and time of day on which to base traffic calculations. You can set times for typical conditions by 15-minute intervals for a 24-hour period.
- Click Create areas.
The threshold area is shown on the map and saved in your project under Threshold areas (sites). Once the threshold area has been created, you can view details in the results table and in the workflow panel.
- Optionally, in the workflow panel, hover your cursor over an item to view more information. If you created multiple threshold areas, use the drop-down menu to view details for different areas.
You can click Export to Excel to create an Excel document with the analysis results. The exported document contains two worksheets: one containing a summary of the analysis, and one containing the details of the analysis.
- To perform further actions using the threshold area, click Finish.
You can run reports and infographics on the site or create new threshold areas.
- To exit the workflow, click I'm done.
Usage notes
This workflow creates areas on the map based on parameters that you define. To change the default values for the threshold areas workflow, see Set preferences.
Parameters
For more information on each parameter in the threshold areas workflow, see the following:
| Parameter | Description | Notes |
|---|---|---|
Variable | What you are measuring | When choosing a variable, consider the following:
Examples:
|
Threshold value | The amount of the variable you are seeking | When specifying threshold values, consider the following:
Example:
|
Target percent difference | How close the final calculation should be to the threshold value | When specifying the target percent difference, consider the following:
Example:
|
Increment size | How rapidly the area expands as the measurement is calculated | When specifying the increment size, consider the following:
Example:
|
Credit usage
The threshold areas workflow uses credits. To understand credit calculation, see the following:
| Area type | Credit usage | Example |
|---|---|---|
Rings | Credits are consumed for each GeoEnrichment request per iteration (0.01 credits). A threshold ring may take approximately 15 iterations to reach one ring polygon. | If you run threshold rings for 10 locations, each location may need 15 iterations to reach the threshold value, resulting in 1.5 credits used. |
Drive times | Credits are consumed for each drive-time area per iteration (0.5 credits per polygon) and each GeoEnrichment request (0.01 credits per view). A threshold drive time takes approximately 6 to 12 iterations to reach one drive-time polygon. | If you run threshold drive times for two locations, each location may need 10 iterations to reach the threshold value, followed by one GeoEnrichment request to retrieve the selected variable, resulting in 10.1 credits used. |
Considerations
Threshold calculations are always necessarily an approximation—when the algorithm runs using real-world conditions, the output differs based on these conditions. There will be cases when the threshold values returned by the algorithm differ from the threshold values you set in the workflow. The values returned may be more or less than the requested threshold value. The following geographic factors affect the area created:
- Population density (for example, densely populated urban areas)
- Actual placement of census block points
- Traffic patterns
If the returned value is not what you expect it to be, try moving the Threshold settings slider to Best precision or manually adjusting the values for Target percent difference and Increment size.
| Best performance | Best precision |
|---|---|
|
|
Set preferences
You can set preferences for ArcGIS Community Analyst in the application preferences. For the threshold areas workflow, you can specify preferences for the threshold variable, threshold values, threshold type, map styling for rings and drive times, and other settings. Administrators can set preferences for the entire organization.
To set the workflow preferences, do the following:
- On the top ribbon, click Preferences .
The Preferences window opens.
- Expand the Maps section, expand the Run analysis section, and click Threshold areas.
- You can set the following preferences:
-
Uncheck the Show threshold areas intro page check box to skip the workflow overview page when you run the analysis.
-
Click Change variable
to select a preferred variable for the analysis. -
Enter values in the Threshold 1, Threshold 2, and Threshold 3 fields to specify threshold preferences.
-
Select Rings or Drive time in the Default threshold type drop-down menu.
-
Use the slider and number fields to specify the settings for the target percent difference and increment size.
-
In the Map styling section, specify the appearance of threshold areas on the map. You can set the fill and border colors, transparency, and label settings for rings and drive times.
-
- To restore the default settings, click Restore defaults.
- To save your changes, click Save or, optionally, click Save and close to close the Preferences window. To view your changes, refresh the app.
Workflow video
Note:
This video was created using ArcGIS Business Analyst Web App, where the user experience and workflows are identical to ArcGIS Community Analyst.