Self hosted website: Dont allow users to continue further into the site unless they allow the geolocation popup

So I have a self hosted website that creates running routes based on their location. The problem is if the user does not click allow to the geolcation popup like in Chrome then they end up with a route from a random place. My question is how can i code it so if they select "no" to the location allow popup the page wont load any further and maybe present a warning to enable location.

Ive spent a good 4 hours reading through questions both on google and on here reference geolocation but nothing on how to perform an action should the visitor say no to the allow location popup.

I'm stuck and my site depends upon this any help would be great thanks.