Creating isochrones in ArcGIS for Desktop?

Question

Is it possible to create isochrones (lines of equal travel time to or from a certain point) in ArcGIS? I have a street network, with the streets having a speed limit attribute, and I need to create a map of travel times to or from a certain point on the network. I know that isochrones in PostGIS and QGIS have been discussed here already, but what about ArcGIS? Also, I would like the final output to be polygons, not lines (i.e., the space between each two isochrones should be a polygon representing all land within a certain travel distance).

I know I can generate a lot of random point features, compute the travel time to each, interpolate that figure between the points, and reclassify the resulting raster into intervals as needed; I've since found that something like this has already been discussed in Using ArcGIS Desktop to create outline (isochrone) around points?, but is there a more elegant way of creating isochrones?

Answer 1

ArcMap's Network Analyst will easily do what you desire.

Begin by opening your street file's attribute table. Create a new field (column) and call it Time. Use the Field Calculator tool to calculate a value for this field based upon the individual line lengths and their respective speed limits (please specify what units you are working with if you need clarification).

Now, let's create a network dataset:

• Within ArcCatalog, navigate to your geodatabase then right-click and select New > Feature Dataset
• Name this Dataset StreetNetwork and remember to specify whatever projection you require
• Right-click on StreetNetwork then select Import > Feature Class (single)
• Name this Feature Class Streets and specify whatever file contains your street data as input
• Now right-click on StreetNetwork and select New > Network Dataset
• Name this Network Dataset Street_ND and make sure that Streets is selected as the feature class that will participate in the network
• Check that the Time attribute is present and finish the creation process

Display the Network Analyst Toolbar (Customise > Toolbars > Network Analyst). Use this to create a New Service Area (select from dropdown list). On the Service Area tab, click Import Facilities and add the point on the network that you wish to travel from. At the top right of the tab, click on the settings button. Ensure that the network Impedance is set to Time. Modify the Cutoff settings to whatever value you desire for your network.

Finish by pressing Run on the Network Analyst Toolbar. The output should be a polygonal area of the region that can be reached along your network within the number of minutes you specified earlier.