From the App Store entry:
The Switch to Android app from Google helps you quickly and securely move your most important data types – photos, videos, contacts, and calendar events — to a brand new Android device without fussy cables.
The app also walks you through other important steps to setting up your device, like turning off iMessage so you don’t miss text messages from friends and family.
For completeness, here's 'Move to iOS' in the Play Store. Both of which are worth a go, though I've tried the latter in the past and not had that happy an experience. Maybe things have moved on.
Back in the real world, of course, I doubt there's much platform switching going on. The vast majority of people on Android or iOS simply buy another phone on the same platform, plus most 'normobs' also end up setting up new phones from scratch as they simply don't know better, often storing just basic contact data on their SIM cards or asking phone shops to help them get contacts over, for example.
Slowly but surely more people are ending up on iPhones though, with 2018's iOS market share of 19% worldwide now being 28%. Perhaps reflecting Google's lack of quality control and the variable attention to detail across the diverse world of Android.