IITC Mobile is a third party app which will allow you to see all existing POI in the game and is a very useful check to carry out before submitting a new pokestop submission to check if POi may already exist in Ingress or if submission will be in a empry cell or atleast 20m away from a existing POi
It is recommended that people download IITC Mobile (including plug-ins) to see all existing POIs and L17 cells.
Below are instructions for Android, which is the original guidance document. Additionally, the Apple fix has also been provided.
How to plan submissions / Android instructions:
https://digiex.net/threads/plan-pokestop-submissions-in-s2-l14-l17-cells-with-iitc-mobile.15729/
iOS:
Download IITC mobile from the app store.
Go to this page:
https://raw.githubusercontent.com/nikolawannabe/s2-cells/master/s2-cells.user.js
Then “view in IITC”.