Apply unique values with alternate symbols

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Apply a unique value with alternate symbols at different scales.

screenshot

Use case

When a layer is symbolized with unique value symbology, you can specify the visible scale range for each unique value. This is an effective strategy to limit the amount of detailed data at smaller scales without having to make multiple versions of the layer, each with a unique definition query.

Once scale ranges are applied to unique values, you can further refine the appearance of features within those scale ranges by establishing alternate symbols to different parts of the symbol class scale range.

How to use the sample

Zoom in and out of the map to see alternate symbols at each scale. The symbology changes according to the following scale ranges: 0-5000, 5000-10000, 10000-20000. To go back to the initial viewpoint, press "Reset Viewpoint".

How it works

  1. Create a featureLayer using the service url and add it to the map's list of operational layers.

  2. Create two alternate symbols (a blue square and a yellow diamond) to be used as alternate symbols. To create an alternate symbol:

    a. Create a symbol using SimpleMarkerSymbol.

    b. Convert the simple marker symbol to a MultilayerSymbol using SimpleMarkerSymbol::toMultilayerSymbol.

    c. Set the valid scale range through reference properties on the multilayer point symbols blue square and yellow diamond by calling MultilayerSymbol::setReferenceProperties(new SymbolReferenceProperties(double minScale, double maxScale, QObject *parent = nullptr));.

  3. Create a third multilayer symbol to be used to create a UniqueValue class.

  4. Create a unique value using the red triangle from step 3 and the list of alternate symbols from step 2.

  5. Create a UniqueValueRenderer and add the unique value from step 4 to it.

  6. Create a purple diamond simple marker and convert it to a multilayer symbol to be used as the default symbol.

  7. Set the default symbol on the unique value renderer to the purple diamond from step 6 using setDefaultSymbol.

  8. Set the fieldNames on the unique value renderer to "req_type".

  9. Apply this unique value renderer to the renderer on feature layer.

Relevant API

  • MultilayerSymbol
  • SimpleMarkerSymbol
  • SymbolReferenceProperties
  • UniqueValue
  • UniqueValueRenderer

About the data

The San Francisco 311 incidents layer in this sample displays point features related to crime incidents such as grafitti and tree damage that have been reported by city residents.

Tags

alternate symbols, multilayer symbol, scale based rendering, simple marker symbol, symbol reference properties, unique value, unique value renderer

Sample Code

ApplyUniqueValuesWithAlternateSymbols.cppApplyUniqueValuesWithAlternateSymbols.cppApplyUniqueValuesWithAlternateSymbols.hApplyUniqueValuesWithAlternateSymbols.qml
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// [WriteFile Name=ApplyUniqueValuesWithAlternateSymbols, Category=Layers]
// [Legal]
// Copyright 2022 Esri.

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0

// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// [Legal]

#ifdef PCH_BUILD
#include "pch.hpp"
#endif // PCH_BUILD

#include "ApplyUniqueValuesWithAlternateSymbols.h"

#include "Basemap.h"
#include "FeatureLayer.h"
#include "Map.h"
#include "MapQuickView.h"
#include "MultilayerPointSymbol.h"
#include "ServiceFeatureTable.h"
#include "SimpleMarkerSymbol.h"
#include "SymbolReferenceProperties.h"
#include "UniqueValueRenderer.h"

using namespace Esri::ArcGISRuntime;

ApplyUniqueValuesWithAlternateSymbols::ApplyUniqueValuesWithAlternateSymbols(QObject* parent /* = nullptr */):
  QObject(parent),
  m_map(new Map(BasemapStyle::ArcGISTopographic, this))
{
  // Create the feature table
  ServiceFeatureTable* featureTable = new ServiceFeatureTable(QUrl("https://sampleserver6.arcgisonline.com/arcgis/rest/services/SF311/FeatureServer/0"), this);

  // Create the feature layer using the feature table
  m_featureLayer = new FeatureLayer(featureTable, this);

  // Add the feature layer to the map
  m_map->operationalLayers()->append(m_featureLayer);

  // This function creates a unique value renderer using
  // one unique value "req_type" that includes a list of
  // alternate symbols for various scales
  createUniqueValueRenderer();
}

ApplyUniqueValuesWithAlternateSymbols::~ApplyUniqueValuesWithAlternateSymbols() = default;

void ApplyUniqueValuesWithAlternateSymbols::init()
{
  // Register the map view for QML
  qmlRegisterType<MapQuickView>("Esri.Samples", 1, 0, "MapView");
  qmlRegisterType<ApplyUniqueValuesWithAlternateSymbols>("Esri.Samples", 1, 0, "ApplyUniqueValuesWithAlternateSymbolsSample");
}

MapQuickView* ApplyUniqueValuesWithAlternateSymbols::mapView() const
{
  return m_mapView;
}

// Set the view (created in QML)
void ApplyUniqueValuesWithAlternateSymbols::setMapView(MapQuickView* mapView)
{
  if (!mapView || mapView == m_mapView)
    return;

  m_mapView = mapView;
  m_mapView->setMap(m_map);

  // Set the initial view point upon opening the sample to focus on an area with a lot of features
  Viewpoint vpCenter = Viewpoint(Point(-13631205.660131, 4546829.846004, SpatialReference::webMercator()), 25000);
  m_mapView->setViewpoint(vpCenter);

  queryCurrentScale();
  emit mapViewChanged();
}

void ApplyUniqueValuesWithAlternateSymbols::createUniqueValueRenderer()
{
  QList<Symbol*> alternateSymbols = createAlternateSymbols();

  double minScale = 5000;
  double maxScale = 0;
  SimpleMarkerSymbol* symbol1 = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle::Triangle, QColor("red"), 30, this);
  MultilayerPointSymbol* multilayerSymbol1 = symbol1->toMultilayerSymbol();
  multilayerSymbol1->setReferenceProperties(new SymbolReferenceProperties(minScale, maxScale, this));

  // Create a unique value with alternate symbols
  UniqueValue* uniqueValue = new UniqueValue("unique value", "unique values based on request type", QVariantList{"Damaged Property"}, multilayerSymbol1, alternateSymbols, this);

  // Create a unique value renderer
  m_uniqueValueRenderer = new UniqueValueRenderer(this);

  // Create and append unique value
  m_uniqueValueRenderer->uniqueValues()->append(uniqueValue);

  m_uniqueValueRenderer->setFieldNames({"req_type"});

  SimpleMarkerSymbol* defaultSym = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle::Diamond, QColor("purple"), 15, this);
  m_uniqueValueRenderer->setDefaultSymbol(defaultSym->toMultilayerSymbol());

  // Set the unique value renderer on the feature layer
  m_featureLayer->setRenderer(m_uniqueValueRenderer);
}

QList<Symbol*> ApplyUniqueValuesWithAlternateSymbols::createAlternateSymbols()
{
  double minScale1 = 10000;
  double maxScale1 = 5000;
  SimpleMarkerSymbol* alternateSymbol1 = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle::Square, QColor("blue"), 45, this);
  MultilayerPointSymbol* alternateSymbolMultilayer1 = alternateSymbol1->toMultilayerSymbol();
  alternateSymbolMultilayer1->setReferenceProperties(new SymbolReferenceProperties(minScale1, maxScale1, this));

  double minScale2 = 20000;
  double maxScale2 = 10000;
  SimpleMarkerSymbol* alternateSymbol2 = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle::Diamond, QColor("yellow"), 30, this);
  MultilayerPointSymbol* alternateSymbolMultilayer2 = alternateSymbol2->toMultilayerSymbol();
  alternateSymbolMultilayer2->setReferenceProperties(new SymbolReferenceProperties(minScale2, maxScale2, this));

  return {alternateSymbolMultilayer1, alternateSymbolMultilayer2};
}

void ApplyUniqueValuesWithAlternateSymbols::resetViewpoint()
{
  if(m_mapView)
  {
    Viewpoint vpCenter = Viewpoint(Point(-13631205.660131, 4546829.846004, SpatialReference::webMercator()), 25000);
    m_mapView->setViewpoint(vpCenter, 5);
  }
}

double ApplyUniqueValuesWithAlternateSymbols::currentScale() const
{
  return m_currentScale;
}

void ApplyUniqueValuesWithAlternateSymbols::queryCurrentScale()
{
  connect(m_mapView, &MapQuickView::viewpointChanged, this, [this](){
    m_currentScale = m_mapView->mapScale();
    emit currentScaleChanged();
  });

}

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