MKOverlay protocol defines a specific type of annotation that represents both a point and an area on a map. Overlay objects are essentially data objects that contain the geographic data needed to represent the map area. For example, overlays can take the form of common shapes such as rectangles and circles. They can also describe polygons and other complex shapes.
- iOS 4.0+
- macOS 10.9+
- tvOS 9.2+
You use overlays to layer more sophisticated content on top of a map view. For example, you could use an overlay to show the boundaries of a national park or trace a bus route along city streets. The Map Kit framework defines several concrete classes that conform to this protocol and define standard shapes.
Because overlays are also annotations, they have similar usage pattern to annotations. When added to a map view using the
add(_:) method, that view detects whenever the overlay’s defined region intersects the visible portion of the map. At that point, the map view asks its delegate to provide a special overlay view to draw the visual representation of the overlay. If you add an overlay to a map view as an annotation instead, it is treated as an annotation with a single point.