This script is an add-on for Ingress Intel Total Conversion (IITC) and will not work without it.
Once the plugin is installed, selecting a portal will draw a 500 meter ring around that portal and draw all Level 16 S2 grid cells that intersect with that circle. All portals within those cells will be highlighted. Any portal that would be a one-way jump from the selected portal will have an additional red highlight.
Additionally, portals can be marked as part of the current route and all portals marked in this way will display on the map with the Drone icon. This mark is saved when the page is refreshed.
Once you've created a route you can save or reset it, saved routes can be exported/imported and loaded for future use.
Selecting the "Drone Grid Settings" Option in the sidebar will show a variety of configuration options: