It looks like you’re using an MKPolygon even though you’re only drawing a single point, with the same latitude and longitude. I think it would be better to use an MKCircle for a single point.
func drawLocation(_ loc: CLLocation)
{
let center = CLLocationCoordinate2D(latitude: loc.coordinate.latitude, longitude: loc.coordinate.longitude)
let circle = MKCircle(center: center, radius: 4)
DispatchQueue.main.async(execute: {
self.mapView.add(circle)
})
}
func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer
{
if overlay is MKCircle
{
let circleView = MKCircleRenderer(circle: overlay)
circleView.lineWidth = 4
circleView.strokeColor = UIColor(red: 30/255.0, green: 12/255.0, blue: 242/255.0, alpha: 0.4)
return circleView
}
return nil
}
As you say, the zooming feature in and out is what could cause this glitch because the points when you zoom in may look more like a polygon, and when you zoom out the renderer still has polygon artefacts but is now rendering only a single coordinate.
Usually it’s better to use a polygon to render points which are spaced further apart, this helps the renderer since the map renders on a tile-by-tile basis which makes it easy to distinguish points in the polygon. For multiple points which are very close together then we can consider grouping them to use a larger radius MKCircle. You can also consider setting isZoomEnabled to false for the MKMapView and setting a fixed MKCoordinateRegion at the desired zoom level to avoid these rendering artefacts.