Helper Extensions for zooming Annotations and Overlays with an offset from the center of the map.

MKCoordinateRegion+OffsetZoomHelpers.swift

extension MKCoordinateRegion {
	/// Initialize a `MKCoordinateRegion` from a set of `MKAnnotations`
	/// - Parameter annotations: Annotations
	init(for annotations: [MKAnnotation]) {
		var minLat: CLLocationDegrees = 90.0
		var maxLat: CLLocationDegrees = -90.0
		var minLon: CLLocationDegrees = 180.0
		var maxLon: CLLocationDegrees = -180.0
		
		for annotation in annotations {
			let lat = Double(annotation.coordinate.latitude)
			let long = Double(annotation.coordinate.longitude)
			if lat < minLat {
				minLat = lat
			}
			if long < minLon {
				minLon = long
			}
			if lat > maxLat {
				maxLat = lat
			}
			if long > maxLon {
				maxLon = long
			}
		}
		
		var span = MKCoordinateSpan(
			latitudeDelta: (maxLat - minLat),
			longitudeDelta: (maxLon - minLon)
		)
		
		let center = CLLocationCoordinate2D(
			latitude: maxLat - span.latitudeDelta / 2,
			longitude: maxLon - span.longitudeDelta / 2
		)
		
		// Apply padding
		span.latitudeDelta = span.latitudeDelta * 1.2
		span.longitudeDelta = span.longitudeDelta * 1.2
		
		self.init(center: center, span: span)
	}
	
	/// Initialize a `MKCoordinateRegion` from an `MKOverlay`
	/// - Parameter annotations: Annotations
	init(for overlay: MKOverlay) {
		let mapRect = overlay.boundingMapRect
		
		let paddedMapRect = mapRect.insetBy(dx: mapRect.width * -0.16, dy: mapRect.height * -0.16)
		
		self.init(paddedMapRect)
	}
}

MKMapView+OffsetZoom.swift

import Foundation
import MapKit

extension MKMapView {
	/// Zooms to fit all the specified annotations on screen.
	/// Offsets the center point based on landscape or portrait mode.
	/// - Parameters:
	///   - annotations: annotations to zoom.
	///   - zoomLevel: how many meters around the point to show (this does nothing if there is more than one annotation).
	///   - offsetFromCenter: number between -1 and 1.
	///   - animated: animate the zoom.
	///
	/// - Note:
	///		If you use an offset of 0.25, the center will be in the top 25% of the screen in portrait mode.
	///		In landscape mode it will be in the right 25% of the screen.
	func offsetZoomTo(
		annotations: [MKAnnotation],
		zoomLevel: CLLocationDistance,
		offsetFromCenter: Double,
		animated: Bool
	) {
		guard !annotations.isEmpty else { return }
		
		let isLandscape: Bool
		
		switch UIDevice.current.orientation {
		case .landscapeLeft, .landscapeRight:
			isLandscape = true
		default:
			isLandscape = false
		}
		
		var annotationRegion: MKCoordinateRegion
		
		if annotations.count == 1,
		   let first = annotations.first {
			annotationRegion = MKCoordinateRegion(
				center: first.coordinate,
				latitudinalMeters: zoomLevel,
				longitudinalMeters: zoomLevel
			)
		} else {
			annotationRegion = MKCoordinateRegion(for: annotations)
		}
		
		// We need to get the map view's region that will enclose the annotation region.
		let fullMapRegion = regionThatFits(annotationRegion)
		
		var newCenter = fullMapRegion.center
		
		// Offset the map center point.
		if isLandscape {
			newCenter.longitude = newCenter.longitude - fullMapRegion.span.longitudeDelta * offsetFromCenter
		} else {
			newCenter.latitude = newCenter.latitude - fullMapRegion.span.latitudeDelta * offsetFromCenter
		}
		
		setRegion(
			MKCoordinateRegion(
				center: newCenter,
				span: fullMapRegion.span
			),
			animated: true
		)
	}
	
	/// Zooms to fit all the specified annotations on screen.
	/// Offsets the center point based on landscape or portrait mode.
	/// - Parameters:
	///   - annotations: annotations to zoom.
	///   - offsetFromCenter: number between -1 and 1.
	///   - animated: animate the zoom.
	///
	/// - Note:
	///		If you use an offset of 0.25, the center will be in the top 25% of the screen in portrait mode.
	///		In landscape mode it will be in the right 25% of the screen.
	func offsetZoomTo(
		overlay: MKOverlay,
		offsetFromCenter: Double,
		animated: Bool
	) {
		let isLandscape: Bool
		
		switch UIDevice.current.orientation {
		case .landscapeLeft, .landscapeRight:
			isLandscape = true
		default:
			isLandscape = false
		}
		
		// We need to get the map view's region that will enclose the annotation region.
		let fullMapRegion = regionThatFits(MKCoordinateRegion(for: overlay))
		
		
		var newSpan: MKCoordinateSpan = fullMapRegion.span
		
		// I've found that landscape needs more padding to prevent things from being cutoff...
		if isLandscape {
			newSpan.longitudeDelta = newSpan.longitudeDelta * 1.75
			newSpan.latitudeDelta = newSpan.latitudeDelta * 1.75
		}
		
		var newCenter = fullMapRegion.center
		
		// Offset the map center point.
		if isLandscape {
			newCenter.longitude = newCenter.longitude - newSpan.longitudeDelta * offsetFromCenter
		} else {
			newCenter.latitude = newCenter.latitude - newSpan.latitudeDelta * offsetFromCenter
		}
		
		setRegion(
			MKCoordinateRegion(
				center: newCenter,
				span: newSpan
			),
			animated: true
		)
	}
}