How can I estimate a user's physical location?

I would like to know the ways in which I could estimate a user's physical location without having to request geolocation permissions on their browser. For example sites like cragslist, and gmail can estimate my location however I never granted them geolocation permissions through my browser.

So how are they doing this? through my IP? which service "translates" the IP to a physical location estimate? and can this be done exclusively on the client side?