Style a feature layer

Learn how to apply renderers and label definitions to a feature layer based on attribute values.

style a feature layer

Applications can display feature layer data with different styles to enhance the visualization. The type of Renderer you choose depends on your application. A SimpleRenderer applies the same symbol to all features, a UniqueValueRenderer applies a different symbol to each unique attribute value, and a ClassBreaksRenderer applies a symbol to a range of numeric values. Renderers are responsible for accessing the data and applying the appropriate symbol to each feature when the layer draws. You can also use a LabelDefinition to show attribute information for features. Visit the Styles and data visualization documentation to learn more about styling layers.

You can also author, style and save web maps, web scenes, and layers as portal items and then add them to the map in your application. Visit the following tutorials to learn more about adding portal items.

In this tutorial, you will apply different renderers to enhance the visualization of three feature layers with data for the Santa Monica Mountains: Trailheads with a single symbol, Trails based on elevation change and bike use, and Parks and Open Spaces based on the type of park.

Prerequisites

The following are required for this tutorial:

An ArcGIS account to access API keys. If you don't have an account, sign up for free.
Your system meets the system requirements.
The ArcGIS Runtime API for Qt is installed.

Steps

Open the project in Qt Creator

To start this tutorial, complete the Display a map tutorial or download and unzip the solution.
Open the display_a_map project in Qt Creator.
If you downloaded the Display a map solution, set your API key.
An API Key enables access to services, web maps, and web scenes hosted in ArcGIS Online.
1. Go to your developer dashboard to get your API key. For these tutorials, use your default API key. It is scoped to include all of the services demonstrated in the tutorials.
2. In the Projects window, in the Sources folder, open the main.cpp file.
3. Modify the code to set the API key. Paste the API key, acquired from your dashboard, between the quotes. Then save and close the file.
  main.cpp
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Add needed classes and declarations

In the Projects window, open the Headers folder. Open the display_a_map.h file.

Add the LabelDefinition and FeatureLayer classes to the namespace.

Display_a_map.h
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namespace ArcGISRuntime
{
class Map;
class MapQuickView;

class LabelDefinition;
class FeatureLayer;

Add the declarations for methods you will create.

Display_a_map.h
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private:
  Esri::ArcGISRuntime::MapQuickView* mapView() const;
  void setMapView(Esri::ArcGISRuntime::MapQuickView* mapView);

  void setupViewpoint();

  void addOpenSpaceLayer();
  void addTrailsLayer();
  void addNoBikeTrailsLayer();
  void addBikeOnlyTrailsLayer();
  void addTrailheadsLayer();
  Esri::ArcGISRuntime::FeatureLayer* addFeatureLayer(const QUrl& url);
  Esri::ArcGISRuntime::LabelDefinition* makeLabelDefinition();

Save and close the file.

Create a function to add a feature layer

A feature layer can be added from a feature service hosted in ArcGIS Online. Each feature layer contains features with a single geometry type (point, line, or polygon), and a set of attributes. Once added to the map, feature layers can be symbolized, styled, and labeled in a variety of ways.

Next, you will create a helper method to add a layer to the map's collection of operational layers. You will use this helper method throughout the tutorial as you add and symbolize various layers.

Add a helper method named addFeatureLayer() that takes a feature service URL as an argument.

Display_a_map.cpp
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void Display_a_map::setupViewpoint()
{
    const Point center(-118.80543, 34.02700, SpatialReference::wgs84());
    const Viewpoint viewpoint(center, 100000.0);
    m_mapView->setViewpoint(viewpoint);

}

// Create a new function that creates a feature layer and appends it to the operational layers and the m_map.
FeatureLayer* Display_a_map::addFeatureLayer(const QUrl& url)
{
    ServiceFeatureTable* serviceFeatureTable = new ServiceFeatureTable(url, this);
    FeatureLayer* featureLayer = new FeatureLayer(serviceFeatureTable, this);
    m_map->operationalLayers()->append(featureLayer);
    return featureLayer;
}
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Add include statements to access the classes used in addFeatureLayer().

Display_a_map.cpp
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#include "Basemap.h"
#include "Map.h"
#include "MapQuickView.h"

#include "FeatureLayer.h"
#include "ServiceFeatureTable.h"

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Add a layer with a unique value renderer

Create a method that creates a variable to store a feature service URL. Create a Parks and Open Spaces feature layer using that variable and then apply a different symbol for each type of park area displayed.

Add a new method named addOpenSpaceLayer(), after the newly added addFeatureLayer() method.

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void Display_a_map::addOpenSpaceLayer()
{
    // Create a parks and open spaces feature layer.
    QUrl parksAndOpenSpacesQUrl("https://services3.arcgis.com/GVgbJbqm8hXASVYi/ArcGIS/rest/services/Parks_and_Open_Space/FeatureServer/0");
    FeatureLayer* featureLayer = addFeatureLayer(parksAndOpenSpacesQUrl);

    // Create fill symbols.
    SimpleFillSymbol* purpleFillSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle::Solid, QColor("purple"), this);
    SimpleFillSymbol* greenFillSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle::Solid, QColor("green"), this);
    SimpleFillSymbol* blueFillSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle::Solid, QColor("blue"), this);
    SimpleFillSymbol* redFillSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle::Solid, QColor("red"), this);

    // Create a unique value for natural areas, regional open spaces, local parks & regional recreation parks.
    UniqueValue* naturalAreas = new UniqueValue("Natural Areas", "Natural Areas", {"Natural Areas"}, purpleFillSymbol, this);
    UniqueValue* regionalOpenSpace = new UniqueValue("Regional Open Space", "Regional Open Space", {"Regional Open Space"}, greenFillSymbol, this);
    UniqueValue* localPark = new UniqueValue("Local Park", "Local Park", {"Local Park"}, blueFillSymbol, this);
    UniqueValue* regionalRecreationPark = new UniqueValue("Regional Recreation Park", "Regional Recreation Park",
                                                          {"Regional Recreation Park"}, redFillSymbol, this);

    // Create and assign a unique value renderer to the feature layer.
    UniqueValueRenderer* openSpacesUniqueValueRenderer = new UniqueValueRenderer("Open Spaces", nullptr, {"TYPE"},
                                                                                 {naturalAreas, regionalOpenSpace, localPark, regionalRecreationPark }, this);
    featureLayer->setRenderer(openSpacesUniqueValueRenderer);

    // Set the layer opacity to semi-transparent.
    featureLayer->setOpacity(0.25f);
}
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Add include statements to access the classes used in addOpenSpaceLayer().

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#include "Basemap.h"
#include "Map.h"
#include "MapQuickView.h"

#include "FeatureLayer.h"
#include "ServiceFeatureTable.h"

#include <QUrl>
#include "SimpleFillSymbol.h"
#include "UniqueValueRenderer.h"

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Update setupViewpoint() to call the new addOpenSpaceLayer() method.

Display_a_map.cpp
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void Display_a_map::setupViewpoint()
{
    const Point center(-118.80543, 34.02700, SpatialReference::wgs84());
    const Viewpoint viewpoint(center, 100000.0);
    m_mapView->setViewpoint(viewpoint);

    addOpenSpaceLayer();
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Press <Ctrl+R> to run the app.

When the app opens, Parks and Open Spaces feature layer is added to the map. The map displays the different types of parks and open spaces with four unique symbols.

Add a layer with a class breaks renderer

Create a method to apply a different symbol for each of the five ranges of elevation gain to the Trails feature layer.

Add a new method named addTrailsLayer().

A ClassBreak assigns a symbol to a range of values.

For this example, the renderer uses each feature's ELEV_GAIN attribute value to classify it into a defined range (class break) and apply the corresponding symbol.

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void Display_a_map::addTrailsLayer()
{
    FeatureLayer* featureLayer = addFeatureLayer(trailsQUrl);
    // Create five line symbols to display class breaks.
    SimpleLineSymbol* firstClassSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle::Solid, QColor("purple"), 3, this);
    SimpleLineSymbol* secondClassSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle::Solid, QColor("purple"), 4, this);
    SimpleLineSymbol* thirdClassSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle::Solid, QColor("purple"), 5, this);
    SimpleLineSymbol* fourthClassSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle::Solid, QColor("purple"), 6, this);
    SimpleLineSymbol* fifthClassSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle::Solid, QColor("purple"), 7, this);

    // Create five class breaks.
    ClassBreak* firstClassBreak = new ClassBreak("Under 500", "0 - 500", 0.0, 500.0, firstClassSymbol, this);
    ClassBreak* secondClassBreak = new ClassBreak("501 to 1000", "501 - 1000", 501.0, 1000.0, secondClassSymbol, this);
    ClassBreak* thirdClassBreak = new ClassBreak("1001 to 1500", "1001 - 1500", 1001.0, 1500.0, thirdClassSymbol, this);
    ClassBreak* fourthClassBreak = new ClassBreak("1501 to 2000", "1501 - 2000", 1501.0, 2000.0, fourthClassSymbol, this);
    ClassBreak* fifthClassBreak = new ClassBreak("2001 to 2300", "2001 to 2300", 2001.0, 2300.0, fifthClassSymbol, this);
    QList<ClassBreak*> elevationBreaks = {firstClassBreak, secondClassBreak, thirdClassBreak, fourthClassBreak, fifthClassBreak};

    // Create and assign a class breaks renderer to the feature layer.
    ClassBreaksRenderer* elevationClassBreaksRenderer = new ClassBreaksRenderer("ELEV_GAIN", elevationBreaks, this);
    featureLayer->setRenderer(elevationClassBreaksRenderer);

    // Set the layer opacity to semi-transparent.
    featureLayer->setOpacity(0.75);
}
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Add a global QUrl variable for the trails feature service.

Display_a_map.cpp
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MapQuickView* Display_a_map::mapView() const
{
    return m_mapView;
}

QUrl trailsQUrl("https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/Trails/FeatureServer/0");
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Add include statements to access the classes used in addTrailsLayer().

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#include "Basemap.h"
#include "Map.h"
#include "MapQuickView.h"

#include "FeatureLayer.h"
#include "ServiceFeatureTable.h"

#include <QUrl>
#include "SimpleFillSymbol.h"
#include "UniqueValueRenderer.h"

#include "SimpleLineSymbol.h"
#include <QList>
#include "ClassBreaksRenderer.h"

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Update setupViewpoint() to call the new addTrailsLayer() method.

Display_a_map.cpp
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void Display_a_map::setupViewpoint()
{
    const Point center(-118.80543, 34.02700, SpatialReference::wgs84());
    const Viewpoint viewpoint(center, 100000.0);
    m_mapView->setViewpoint(viewpoint);

    addOpenSpaceLayer();

    addTrailsLayer();
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Press <Ctrl+R> to run the app.

When the app opens, the Trails feature layer is added to the map. The map displays trails with different symbols depending on trail elevation.

Add layers that leverage definition expressions

You can use a definition expression to define a subset of features to display. Features that do not meet the expression criteria are not displayed by the layer. In the following steps, you will create two methods that use a definition expression to apply a symbol to a subset of features in the Trails feature layer.

FeatureLayer::definitionExpression() uses a SQL expression to limit the features available for query and display. Your code will create two layers that each display a different subset of trails based on the value for the USE_BIKE field. Trails that allow bikes will be symbolized with a blue symbol ("USE_BIKE = 'Yes'") and those that don't will be red ("USE_BIKE = 'No'"). Another way to symbolize these features would be to create a UniqueValueRenderer that applies a different symbol for these values.

Add a method named addBikeOnlyTrailsLayer() with a definition expression to filter for trails that permit bikes.

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void Display_a_map::addBikeOnlyTrailsLayer()
{
    // Create a trails feature layer and add it to the map view.
    FeatureLayer* featureLayer = addFeatureLayer(trailsQUrl);

    // Write a definition expression to filter for trails that permit the use of bikes.
    featureLayer->setDefinitionExpression("USE_BIKE = 'Yes'");

    // Create and assign a simple renderer to the feature layer.
    SimpleLineSymbol* bikeTrailSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle::Dot, QColor("blue"), 2, this);
    SimpleRenderer* bikeTrailRenderer = new SimpleRenderer(bikeTrailSymbol, this);
    featureLayer->setRenderer(bikeTrailRenderer);
}
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Add another method named addNoBikeTrailsLayer() with a definition expression to filter for trails that don't allow bikes.

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void Display_a_map::addNoBikeTrailsLayer()
{
    // Create a trails feature layer and add it to the map view.
    FeatureLayer* featureLayer = addFeatureLayer(trailsQUrl);

    // Write a definition expression to filter for trails that don't permit the use of bikes.
    featureLayer->setDefinitionExpression("USE_BIKE = 'No'");

    // Create and assign a simple renderer to the feature layer.
    SimpleLineSymbol* noBikeTrailSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle::Dot, QColor("red"), 2, this);
    SimpleRenderer* noBikeTrailRenderer = new SimpleRenderer(noBikeTrailSymbol, this);
    featureLayer->setRenderer(noBikeTrailRenderer);
}
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Add include statements to access the classes used in addBikeOnlyTrailsLayer() and addNoBikeTrailsLayer().
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ArcGIS Runtime API for Qt