Information for Style Authors

A style defines a map view’s content and appearance. If you’ve authored a style using MapTiler Customize’s Styles editor or as JSON in a text editor, you can use that style in this SDK and manipulate it afterwards in code. This document provides information you can use to ensure a seamless transition from MapTiler Customize to your application.

Designing for macOS

When designing your style, consider the context in which your application shows the style. There are a number of considerations specific to macOS that may not be obvious when designing your style in MapTiler Customize on the Web. A map view is essentially a graphical user interface element, so many of same issues in user interface design also apply when designing a map style.

Color

Ensure sufficient contrast in your application’s user interface when your map style is present. Standard user interface elements such as toolbars, sidebars, and sheets often overlap the map view with a translucent, blurred background, so make sure the contents of these elements remain legible with the map view underneath. If you intend your style to be used in the dark, consider the impact that Night Shift may have on your style’s colors.

Typography and graphics

Design sprite images and choose font weights that look crisp on both standard-resolution displays and Retina displays. This SDK supports the same resolutions as macOS. Standard-resolution displays are often found on external monitors. Even with built-in screens, some of your users may use the Larger Text option in Display Preferences, which is essentially standard resolution, to make text easier to read.

Icon and text labels should be legible regardless of the map’s orientation. By default, this SDK makes it easy for your users to rotate or tilt the map using multitouch trackpad gestures or keyboard shortcuts. If you do not intend your design to accommodate rotation and tilting, disable these gestures using the MGLMapView.rotateEnabled and MGLMapView.pitchEnabled properties, respectively, or the corresponding inspectables in Interface Builder.

Interactivity

Pay attention to whether elements of your style appear to be interactive. An icon with a shadow or shading effect may appear to be clickable. You can make an icon or text label interactive by installing a gesture recognizer and performing feature querying (e.g., -[MGLMapView visibleFeaturesAtPoint:]) to get details about the selected feature. You can install cursor or tooltip tracking rectangles to indicate interactive features as an alternative to prominent hover effects.

Make sure your users can easily distinguish any interactive elements from the surrounding map, such as pins or a route line. If your application supports printing, consider using the runtime styling API to optimize your style for ink economy before printing the map view.

For more information about user interface design, consult Apple’s macOS Human Interface Guidelines.

Applying your style

You set an MGLMapView object’s style either in code, by setting the MGLMapView.styleURL property, or in Interface Builder, by setting the “Style URL” inspectable. The URL must point to a local or remote style JSON file. The style JSON file format is defined by the GL Style Specification. This SDK supports the functionality defined by version 8 of the specification unless otherwise noted in the style specification documentation.

Manipulating the style at runtime

The runtime styling API enables you to modify every aspect of a style dynamically as a user interacts with your application. The style itself is represented at runtime by an MGLStyle object, which provides access to various MGLSource and MGLStyleLayer objects that represent content sources and style layers, respectively.

The names of runtime styling classes and properties on macOS are generally consistent with the style specification and MapTiler Customize’s Styles editor. Any exceptions are listed in this document.

To avoid conflicts with Objective-C keywords or Cocoa terminology, this SDK uses the following terms for concepts defined in the style specification:

Specifying the map’s content

Each source defined by a style JSON file is represented at runtime by a content source object that you can use to initialize new style layers. The content source object is a member of one of the following subclasses of MGLSource:

Tile sources

Raster and vector sources may be defined in TileJSON configuration files. This SDK supports the properties defined in the style specification, which are a subset of the keys defined in version 2.1.0 of the TileJSON specification. As an alternative to authoring a custom TileJSON file, you may supply various tile source options when creating a raster or vector source. These options are detailed in the MGLTileSourceOption documentation:

Shape sources

Shape sources also accept various options. These options are detailed in the MGLShapeSourceOption documentation:

To create a shape source from local GeoJSON data, first convert the GeoJSON data into a shape, then use the -[MGLShapeSource initWithIdentifier:shape:options:] method.

Configuring the map content’s appearance

Each layer defined by the style JSON file is represented at runtime by a style layer object, which you can use to refine the map’s appearance. The style layer object is a member of one of the following subclasses of MGLStyleLayer:

You configure layout and paint attributes by setting properties on these style layer objects. The property names generally correspond to the style JSON properties, except for the use of camelCase instead of kebab-case. Properties whose names differ from the style specification are listed below:

Circle style layers

Fill style layers

Line style layers

Raster style layers

Symbol style layers

Setting attribute values

Each property representing a layout or paint attribute is set to an MGLStyleValue object, which is either an MGLConstantStyleValue object (for constant values) or an MGLStyleFunction object (for style functions). The style value object is a container for the raw value or function parameters that you want the attribute to be set to.

Constant style values

In contrast to the JSON type that the style specification defines for each layout or paint property, the style value object often contains a more specific Foundation or Cocoa type. General rules for attribute types are listed below. Pay close attention to the SDK documentation for the attribute you want to get or set.

For padding attributes, note that the arguments to NSEdgeInsetsMake() in Objective-C and EdgeInsets(top:left:bottom:right:) in Swift are specified in counterclockwise order, in contrast to the clockwise order defined by the style specification.

Additionally, on macOS, a screen coordinate of (0, 0) is located at the lower-left corner of the screen. Therefore, a positive CGVector.dy means an offset or translation upward, while a negative CGVector.dy means an offset or translation downward. This is the reverse of how CGVector is interpreted on iOS.

Style functions

A style function allows you to vary the value of a layout or paint attribute based on the zoom level, data provided by content sources, or both. For more information about style functions, see “Using Style Functions at Runtime”.

Each kind of style function is represented by a distinct class, but you typically create style functions as you create any other style value, using class methods on MGLStyleValue:

The documentation for each individual style layer property indicates the kinds of style functions that are enabled for that property.

When you create a style function, you specify an interpolation mode and a series of stops. Each stop determines the effective value displayed at a particular zoom level (for camera functions) or the effective value on features with a particular attribute value in the content source (for source functions). The interpolation mode tells the SDK how to calculate the effective value between any two stops:

Filtering sources

You can filter a shape or vector source by setting the MGLVectorStyleLayer.predicate property to an NSPredicate object. Below is a table of style JSON operators and the corresponding operators used in the predicate format string:

See the MGLVectorStyleLayer.predicate documentation for a full description of the supported operators and operand types.