Displaying overlays on a map

At a glance

Project structure

Source bundle/
└── MapKitOverlays/
    ├── Supporting Files/
    │   ├── AppDelegate.swift
    │   └── SceneDelegate.swift
    ├── OverlayViewController.swift
    ├── PrimaryColumnTableViewController.swift
    ├── Custom Renderer/
    │   ├── PeakGroundAccelerationOverlayRenderer.swift
    │   ├── GridGeometry.swift
    │   └── PeakGroundAccelerationGrid.swift
    ├── MultiPolygon/
    │   ├── EventAnnotationView.swift
    │   └── EventDataSource.swift
    ├── LocationData.swift
    └── Map Tiles/
        ├── CustomLoadingTileOverlay.swift
        └── TileCoordinateOverlay.swift

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: Swift.
• The verified tree contains 9 project/configuration file(s) and 16 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["OverlayViewController"]
    N3["PeakGroundAccelerationOverlayRenderer"]
    N4["MapKit APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

MapKitOverlays/Supporting Files/AppDelegate.swift:10 — architecture anchor

@main
class AppDelegate: UIResponder, UIApplicationDelegate {

}

Interpretation

The arrows summarize the source-visible entry, role-named types or folders, and framework direction; when nodes come from structural folders, the sequence is a high-level interpretation rather than proof that every adjacent node calls the next. Ownership is claimed only where the next section cites a stored property or assignment. The diagram is intentionally limited to the dominant path into MapKit.

Ownership and state

classDiagram
    OverlayViewController o-- ExampleOverlay : currentExample
    OverlayViewController o-- MKMapView : mapView
    OverlayViewController o-- UIBarButtonItem : layerMenuButton
    OverlayViewController *-- UIEdgeInsets : standardPadding

Ownership evidence

MapKitOverlays/OverlayViewController.swift:37 — stored dependency or nearest verified ownership anchor

class OverlayViewController: UIViewController {
    // ...
    var currentExample: ExampleOverlay?
    // ...
}

Composition arrows indicate a source-visible construction expression or locally owned value state; aggregation means the owner stores or receives a dependency without proving exclusive lifetime ownership.

Concurrency, scheduling, and thread safety

Evidence limit: actor isolation, async/await, or Task creation does not by itself prove background-thread execution; Sendable conformance alone does not prove thread-safe mutation.

@MainActor/MainActor.run, DispatchQueue.main, and RunLoop.main are reported as distinct isolation, queue, and event-loop mechanisms. A plain Task is kept separate from Task.detached; neither is labeled as a background thread.

Reference code

MapKitOverlays/Custom Renderer/PeakGroundAccelerationGrid.swift:31 — representative execution boundary

    init?(gridedDataFile: URL) async {
        var rawData: String!
        // ...
    }

State propagation, frameworks, and dependencies

Evidence limit: an import proves a source-level compilation dependency at the cited line; it does not prove runtime use, architectural adoption, or whether a Swift package is a direct application dependency.

receive(on:) describes downstream delivery scheduling, while subscribe(on:) describes upstream subscription/request/cancel scheduling. An import Combine alone establishes neither behavior nor a Store, reducer, Redux, or other application architecture.

Class and protocol design

MapKitOverlays/Supporting Files/AppDelegate.swift:11 — representative type boundary

@main
class AppDelegate: UIResponder, UIApplicationDelegate {

}

No local protocol conformance is claimed as protocol-oriented design; external framework conformances are listed only as dependencies.

Access control

Reference code

MapKitOverlays/BlendModeExample.swift:40 — representative boundary

    private func createAndDisplayBlendModeMapOverlays(includeDesaturationMask: Bool = true, includeColorBurn: Bool = true) {
        removeOverlays()
        // ...
    }

Swift declarations without a modifier are internal; explicit private, fileprivate, private(set), public, or open entries above are interpreted by language semantics. Objective-C/C samples instead rely on header and implementation boundaries, which are not equivalent to Swift lexical privacy.

Logic ownership and placement

Design patterns

Naming conventions

• Types: Controller: OverlayViewController, PrimaryColumnTableViewController; DataSource: EventDataSource; Delegate: AppDelegate, SceneDelegate; Renderer: PeakGroundAccelerationOverlayRenderer; View: EventAnnotationView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: viewDidLoad, viewDidAppear, traitCollectionDidChange, displayExample, removeOverlays, setupStandardMenu, mapView, prepare.
• Files: MapKitOverlays/Supporting Files/AppDelegate.swift, MapKitOverlays/OverlayViewController.swift, MapKitOverlays/PrimaryColumnTableViewController.swift, MapKitOverlays/Custom Renderer/PeakGroundAccelerationOverlayRenderer.swift, MapKitOverlays/MultiPolygon/EventAnnotationView.swift, MapKitOverlays/MultiPolygon/EventDataSource.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches MapKit, UIKit, CoreLocation through a deliberately small high-level chain; the detailed API graph remains inside the cited implementation files.
• Stored-property evidence identifies lifecycle collaboration; it does not by itself prove exclusive object ownership.
• Access-control conclusions separate verified language visibility from the likely design rationale.
• The source does not justify labeling the design protocol-oriented.

Source map

• Official Apple documentation