Show labels on layers

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Display custom labels on a feature layer.

Image of show labels on layers

Use case

Labeling features is useful to visually display a key piece of information or attribute of a feature on a map. For example, you may want to label rivers or streets with their names.

How to use the sample

Pan and zoom around the United States. Labels for congressional districts will be shown in red for Republican districts and blue for Democrat districts. Notice how labels pop into view as you zoom in.

How it works

  1. Create a ServiceFeatureTable using a feature service URL.
  2. Create a FeatureLayer from the service feature table.
  3. Create a TextSymbol to use for displaying the label text.
  4. Create an ArcadeLabelExpression for the label definition.

    • You can use fields of the feature by using $feature.field_name in the expression.
  5. Create a new LabelDefinition from the arcade label expression and text symbol.
  6. Add the definition to the feature layer with featureLayer.LabelDefinitions.Add(labelDefinition) .
  7. Lastly, enable labels on the layer using featureLayer.LabelsEnabled.

Relevant API

  • ArcadeLabelExpression
  • FeatureLayer
  • LabelDefinition
  • TextSymbol

About the data

This sample uses the USA 116th Congressional Districts feature layer hosted on ArcGIS Online.

Additional information

Help regarding the Arcade label expression script for defining a label definition can be found on the ArcGIS Developers site.

Tags

arcade, attribute, deconfliction, label, labeling, string, symbol, text, visualization

Sample Code

ShowLabelsOnLayer.cs
                                                                                                                              
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// Copyright 2021 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.

using Android.App;
using Android.OS;
using Android.Widget;
using Esri.ArcGISRuntime.Data;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Mapping.Labeling;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.UI.Controls;
using System;
using System.Drawing;

namespace ArcGISRuntime.Samples.ShowLabelsOnLayer
{
    [Activity(ConfigurationChanges = Android.Content.PM.ConfigChanges.Orientation | Android.Content.PM.ConfigChanges.ScreenSize)]
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        name: "Show labels on layers",
        category: "Layers",
        description: "Display custom labels on a feature layer.",
        instructions: "Pan and zoom around the United States. Labels for congressional districts will be shown in red for Republican districts and blue for Democrat districts. Notice how labels pop into view as you zoom in.",
        tags: new[] { "arcade", "attribute", "deconfliction", "label", "labeling", "string", "symbol", "text", "visualization" })]
    public class ShowLabelsOnLayer : Activity
    {
        // Create and hold reference to the used MapView.
        private MapView _myMapView;

        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);

            Title = "Show labels on layer";

            // Create the UI, setup the control references and execute initialization.
            CreateLayout();
            Initialize();
        }

        private async void Initialize()
        {
            // Create a map with a light gray canvas basemap.
            Map sampleMap = new Map(BasemapStyle.ArcGISLightGray);

            // Assign the map to the MapView.
            _myMapView.Map = sampleMap;

            // Define the URL string for the feature layer.
            string layerUrl = "https://services.arcgis.com/P3ePLMYs2RVChkJx/arcgis/rest/services/USA_115th_Congressional_Districts/FeatureServer/0";

            // Create a service feature table from the URL.
            ServiceFeatureTable featureTable = new ServiceFeatureTable(new Uri(layerUrl));

            // Create a feature layer from the service feature table.
            FeatureLayer districtFeatureLabel = new FeatureLayer(featureTable);

            // Add the feature layer to the operations layers collection of the map.
            sampleMap.OperationalLayers.Add(districtFeatureLabel);

            try
            {
                // Load the feature layer - this way we can obtain it's extent.
                await districtFeatureLabel.LoadAsync();

                // Zoom the map view to the extent of the feature layer.
                await _myMapView.SetViewpointCenterAsync(new MapPoint(-10846309.950860, 4683272.219411, SpatialReferences.WebMercator), 20000000);

                // create label definitions for each party.
                LabelDefinition republicanLabelDefinition = MakeLabelDefinition("Republican", Color.Red);
                LabelDefinition democratLabelDefinition = MakeLabelDefinition("Democrat", Color.Blue);

                // Add the label definition to the feature layer's label definition collection.
                districtFeatureLabel.LabelDefinitions.Add(republicanLabelDefinition);
                districtFeatureLabel.LabelDefinitions.Add(democratLabelDefinition);

                // Enable the visibility of labels to be seen.
                districtFeatureLabel.LabelsEnabled = true;
            }
            catch (Exception ex)
            {
                new AlertDialog.Builder(this).SetMessage(ex.Message).SetTitle("Error").Show();
            }
        }

        private LabelDefinition MakeLabelDefinition(string partyName, Color color)
        {
            // Create a text symbol for styling the label.
            TextSymbol textSymbol = new TextSymbol
            {
                Size = 12,
                Color = color,
                HaloColor = Color.White,
                HaloWidth = 2,
            };

            // Create a label expression using an Arcade expression script.
            LabelExpression arcadeLabelExpression = new ArcadeLabelExpression("$feature.NAME + \" (\" + left($feature.PARTY,1) + \")\\nDistrict \" + $feature.CDFIPS");

            return new LabelDefinition(arcadeLabelExpression, textSymbol)
            {
                Placement = Esri.ArcGISRuntime.ArcGISServices.LabelingPlacement.PolygonAlwaysHorizontal,
                WhereClause = $"PARTY = '{partyName}'",
            };
        }

        private void CreateLayout()
        {
            // Create a new vertical layout for the app.
            LinearLayout layout = new LinearLayout(this) { Orientation = Orientation.Vertical };

            // Add the map view to the layout.
            _myMapView = new MapView(this);
            layout.AddView(_myMapView);

            // Show the layout in the app.
            SetContentView(layout);
        }
    }
}

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