I wanted to do this for the U.S. using free tools built into Power BI. Since bubble size by distance wasn't an option, I did this at the U.S. county level. Whether this method works for other countries will depend on whether the sort of distance file I started with is available or can be created. If you have latitude and longitude for the center of all areas of interest, you can use a measure in PowerBI to find the distances using the Haversine formula without the need for a file where the distances are already recorded. I found that the U.S. National Bureau of Economic Research offers a file with calculated distances from every U.S. county (FIPS code) to every other U.S. county. Using this list of paired locations with distances, I used this method:
- Leave the first division (county FIPS) list unaltered
- Merge the second division list with a list of the locations of interest
- Create a conditional column based on whether the distance bewteen divisions provided in the file is within the bubble range, in your case, 400 miles. For my need, I used three distance ranges for the conditional column to produce two circle colors and color the background a third color.
- If you want the center of the bubble to be a different color, append a list of the divisions of interest with the distances set to zero from themselves and the conditional column value set to whatever you want to call your locations in the map legend
- To keep only the minimum distances, sort the rows ascending by distance and then remove duplicates
- On the pre-loaded, free Azure map, use the conditional column as the legend
