For Style Authors.md

Information for Style Authors

A style defines a map view’s content and appearance. If you’ve authored a style using Mapbox Studio’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 Mapbox Studio to your application.

Designing for iOS

When designing your style, consider the context in which your application shows the style. There are a number of considerations specific to iOS that may not be obvious when designing your style in Mapbox Studio 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. The user location annotation view, the attribution button, any buttons in callout views, and any items in the navigation bar are influenced by your application’s tint color, so choose a tint color that contrasts well with your map style. 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

Choose font and icon sizes appropriate to iOS devices. iPhones and iPads have smaller screens than the typical browser window in which you would use Mapbox Studio, especially when multitasking is enabled. Your user’s viewing distance may be shorter than on a desktop computer. Some of your users may use the Larger Dynamic Type and Accessibility Text features to increase the size of all text on the device. You can use the runtime styling API to adjust your style’s font and icon sizes accordingly.

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 iOS. Standard-resolution displays are limited to older devices that your application may or may not support, depending on its minimum deployment target.

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 gestures. 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. A text label may look like a tappable button merely due to matching your application’s tint color or the default blue tint color. 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.

Make sure your users can easily distinguish any interactive elements from the surrounding map, such as pins, the user location annotation view, or a route line. Avoid relying on hover effects to indicate interactive elements. Leave enough room between interactive elements to accommodate imprecise tapping gestures.

For more information about user interface design, consult Apple’s iOS Human Interface Guidelines. To learn more about designing maps for mobile devices, see Nathaniel Slaughter's blog post on the subject.

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 Mapbox 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. For more information about the capabilities exposed by the runtime styling API, see “Runtime Styling”.

The names of runtime styling classes and properties on iOS are generally consistent with the style specification and Mapbox Studio’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:

In the style specification	In the SDK
class	style class
filter	predicate
function type	interpolation mode
id	identifier
image	style image
layer	style layer
property	attribute
SDF icon	template image
source	content source

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:

In style JSON	In the SDK
geojson	MGLShapeSource
raster	MGLRasterSource
vector	MGLVectorSource

canvas, image, and video sources are not supported.

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:

In style JSON	In TileJSON	In the SDK
url	—	configurationURL parameter in -[MGLTileSource initWithIdentifier:configurationURL:]
tiles	tiles	tileURLTemplates parameter in -[MGLTileSource initWithIdentifier:tileURLTemplates:options:]
minzoom	minzoom	MGLTileSourceOptionMinimumZoomLevel
maxzoom	maxzoom	MGLTileSourceOptionMaximumZoomLevel
tileSize	—	MGLTileSourceOptionTileSize
attribution	attribution	MGLTileSourceOptionAttributionHTMLString (but consider specifying MGLTileSourceOptionAttributionInfos instead for improved security)
scheme	scheme	MGLTileSourceOptionTileCoordinateSystem

Shape sources

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

In style JSON	In the SDK
data	url parameter in -[MGLShapeSource initWithIdentifier:URL:options:]
maxzoom	MGLShapeSourceOptionMaximumZoomLevel
buffer	MGLShapeSourceOptionBuffer
tolerance	MGLShapeSourceOptionSimplificationTolerance
cluster	MGLShapeSourceOptionClustered
clusterRadius	MGLShapeSourceOptionClusterRadius
clusterMaxZoom	MGLShapeSourceOptionMaximumZoomLevelForClustering

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:

In style JSON	In the SDK
background	MGLBackgroundStyleLayer
circle	MGLCircleStyleLayer
fill	MGLFillStyleLayer
fill-extrusion	MGLFillExtrusionStyleLayer
line	MGLLineStyleLayer
raster	MGLRasterStyleLayer
symbol	MGLSymbolStyleLayer

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

In style JSON	In Objective-C	In Swift
circle-pitch-scale	MGLCircleStyleLayer.circleScaleAlignment	MGLCircleStyleLayer.circleScaleAlignment
circle-translate	MGLCircleStyleLayer.circleTranslation	MGLCircleStyleLayer.circleTranslation
circle-translate-anchor	MGLCircleStyleLayer.circleTranslationAnchor	MGLCircleStyleLayer.circleTranslationAnchor

Fill style layers

In style JSON	In Objective-C	In Swift
fill-antialias	MGLFillStyleLayer.fillAntialiased	MGLFillStyleLayer.isFillAntialiased
fill-translate	MGLFillStyleLayer.fillTranslation	MGLFillStyleLayer.fillTranslation
fill-translate-anchor	MGLFillStyleLayer.fillTranslationAnchor	MGLFillStyleLayer.fillTranslationAnchor

Fill extrusion style layers

In style JSON	In Objective-C	In Swift
fill-extrusion-translate	MGLFillExtrusionStyleLayer.fillExtrusionTranslation	MGLFillExtrusionStyleLayer.fillExtrusionTranslation
fill-extrusion-translate-anchor	MGLFillExtrusionStyleLayer.fillExtrusionTranslationAnchor	MGLFillExtrusionStyleLayer.fillExtrusionTranslationAnchor

Line style layers

In style JSON	In Objective-C	In Swift
line-dasharray	MGLLineStyleLayer.lineDashPattern	MGLLineStyleLayer.lineDashPattern
line-translate	MGLLineStyleLayer.lineTranslation	MGLLineStyleLayer.lineTranslation
line-translate-anchor	MGLLineStyleLayer.lineTranslationAnchor	MGLLineStyleLayer.lineTranslationAnchor

Raster style layers

In style JSON	In Objective-C	In Swift
raster-brightness-max	MGLRasterStyleLayer.maximumRasterBrightness	MGLRasterStyleLayer.maximumRasterBrightness
raster-brightness-min	MGLRasterStyleLayer.minimumRasterBrightness	MGLRasterStyleLayer.minimumRasterBrightness
raster-hue-rotate	MGLRasterStyleLayer.rasterHueRotation	MGLRasterStyleLayer.rasterHueRotation

Symbol style layers

In style JSON	In Objective-C	In Swift
icon-allow-overlap	MGLSymbolStyleLayer.iconAllowsOverlap	MGLSymbolStyleLayer.iconAllowsOverlap
icon-ignore-placement	MGLSymbolStyleLayer.iconIgnoresPlacement	MGLSymbolStyleLayer.iconIgnoresPlacement
icon-image	MGLSymbolStyleLayer.iconImageName	MGLSymbolStyleLayer.iconImageName
icon-optional	MGLSymbolStyleLayer.iconOptional	MGLSymbolStyleLayer.isIconOptional
icon-rotate	MGLSymbolStyleLayer.iconRotation	MGLSymbolStyleLayer.iconRotation
icon-size	MGLSymbolStyleLayer.iconScale	MGLSymbolStyleLayer.iconScale
icon-keep-upright	MGLSymbolStyleLayer.keepsIconUpright	MGLSymbolStyleLayer.keepsIconUpright
text-keep-upright	MGLSymbolStyleLayer.keepsTextUpright	MGLSymbolStyleLayer.keepsTextUpright
text-max-angle	MGLSymbolStyleLayer.maximumTextAngle	MGLSymbolStyleLayer.maximumTextAngle
text-max-width	MGLSymbolStyleLayer.maximumTextWidth	MGLSymbolStyleLayer.maximumTextWidth
symbol-avoid-edges	MGLSymbolStyleLayer.symbolAvoidsEdges	MGLSymbolStyleLayer.symbolAvoidsEdges
text-field	MGLSymbolStyleLayer.text	MGLSymbolStyleLayer.text
text-allow-overlap	MGLSymbolStyleLayer.textAllowsOverlap	MGLSymbolStyleLayer.textAllowsOverlap
text-font	MGLSymbolStyleLayer.textFontNames	MGLSymbolStyleLayer.textFontNames
text-size	MGLSymbolStyleLayer.textFontSize	MGLSymbolStyleLayer.textFontSize
text-ignore-placement	MGLSymbolStyleLayer.textIgnoresPlacement	MGLSymbolStyleLayer.textIgnoresPlacement
text-justify	MGLSymbolStyleLayer.textJustification	MGLSymbolStyleLayer.textJustification
text-optional	MGLSymbolStyleLayer.textOptional	MGLSymbolStyleLayer.isTextOptional
text-rotate	MGLSymbolStyleLayer.textRotation	MGLSymbolStyleLayer.textRotation
icon-translate	MGLSymbolStyleLayer.iconTranslation	MGLSymbolStyleLayer.iconTranslation
icon-translate-anchor	MGLSymbolStyleLayer.iconTranslationAnchor	MGLSymbolStyleLayer.iconTranslationAnchor
text-translate	MGLSymbolStyleLayer.textTranslation	MGLSymbolStyleLayer.textTranslation
text-translate-anchor	MGLSymbolStyleLayer.textTranslationAnchor	MGLSymbolStyleLayer.textTranslationAnchor

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.

In style JSON	In Objective-C	In Swift
Color	UIColor	UIColor
Enum	NSValue (see NSValue(MGLAdditions))	NSValue (see NSValue(MGLAdditions))
String	NSString	String
Boolean	NSNumber.boolValue	Bool
Number	NSNumber.floatValue	Float
Array (-dasharray)	NSArray<NSNumber>	[Float]
Array (-font)	NSArray<NSString>	[String]
Array (-offset, -translate)	NSValue.CGVectorValue	NSValue.cgVectorValue
Array (-padding)	NSValue.UIEdgeInsetsValue	NSValue.uiEdgeInsetsValue

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

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:

In style specification	SDK class	SDK factory method
zoom function	MGLCameraStyleFunction	+[MGLStyleValue valueWithInterpolationMode:cameraStops:options:]
property function	MGLSourceStyleFunction	+[MGLStyleValue valueWithInterpolationMode:sourceStops:attributeName:options:]
zoom-and-property function	MGLCompositeStyleFunction	+[MGLStyleValue valueWithInterpolationMode:compositeStops:attributeName:options:]

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:

In style specification	In the SDK
exponential	MGLInterpolationModeExponential
interval	MGLInterpolationModeInterval
categorical	MGLInterpolationModeCategorical
identity	MGLInterpolationModeIdentity

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:

In style JSON	In the format string
["has", key]	key != nil
["!has", key]	key == nil
["==", key, value]	key == value
["!=", key, value]	key != value
[">", key, value]	key > value
[">=", key, value]	key >= value
["<", key, value]	key < value
["<=", key, value]	key <= value
["in", key, v0, …, vn]	key IN {v0, …, vn}
["!in", key, v0, …, vn]	NOT key IN {v0, …, vn}
["all", f0, …, fn]	p0 AND … AND pn
["any", f0, …, fn]	p0 OR … OR pn
["none", f0, …, fn]	NOT (p0 OR … OR pn)

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