A guide to calculating population catchment areas using the TravelTime plugin for QGIS
If you haven't already installed the TravelTime plugin for QGIS, you can get a free trial API key and download the plugin here
The TravelTime plugin for QGIS can be used in conjunction with other QGIS tools and datasets to run powerful spatial analysis.
One example of this is combining the Time Map tool from TravelTime with a layer of population data, then using the Clip tool to calculate the reachable population within a catchment area.
For short walk-through of how to do this, please watch below:

For more information on how to use the Time Map tools, please see our documentation here.
Full documentation for the corresponding API endpoint can be found here.