Find My Friends exists. Therefore, Apple has access to a pipeline providing real-time location data of your whereabouts, if you use that feature. Apple's privacy policy confirms that they collect "Precise location only to support Find My, and coarse location." Apple complies with law-enforcement subpoena requests about 90% of the time in the US (
https://www.apple.com/legal/transparency/us.html). For comparison, Google's compliance rate is about the same, at 84% (
https://transparencyreport.google.com/user-data/overview). I wouldn't expect those rates to be substantially different; they're both US companies subject to US law.
In other words, cops interested in your whereabouts probably don't care much if you have an iOS or Android-based product. Moreover, the easier subpoena target is your wireless carrier. For their service to work, your carrier must map your billing info to your SIM IMEI (I say "must" lazily; I could imagine a ZKP system that gave out certificates showing that a randomized IMEI is paid up. But the angry privacy mob doesn't seem to be focused on carriers right now, so I don't see why they'd change).
According to anecdotes on the web (I am not a customer of Apple), Find My Friends uses IP geolocation as a GPS fallback. It stands to reason that Apple's ad network has built a similar database. I believe both major networks allow individual users to opt out of that database being used to serve them ads, but I don't know whether that means that the ad networks do not still know where that user is.