# Union

### Description

Example of using the GeometryEngine.Union method to calculate the geometric union of feature geometries and a given polygon. To use this sample, the user draws a polygon over the feature polygons and the system then retrieves the union of the feature geometries and the new polygon. Resulting polygons are shown in a graphics overlay on the map.

Available for Desktop, Store

## Sample Code

``````﻿<UserControl x:Class="ArcGISRuntime.Samples.Desktop.UnionGeometry"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:esri="http://schemas.esri.com/arcgis/runtime/2013">
<Grid x:Name="layoutGrid">
<Grid.Resources>
<BooleanToVisibilityConverter x:Key="BooleanToVisibilityConverter"/>

<esri:SimpleFillSymbol x:Key="FillSymbol" Color="#660000FF" Style="Solid">
<esri:SimpleFillSymbol.Outline>
<esri:SimpleLineSymbol Color="Blue" Width="2" />
</esri:SimpleFillSymbol.Outline>
</esri:SimpleFillSymbol>
</Grid.Resources>

<esri:MapView x:Name="MyMapView" WrapAround="True">
<esri:Map InitialViewpoint="-15053000,2749000,-6540000,6590000">
<esri:ArcGISTiledMapServiceLayer
ServiceUri="http://services.arcgisonline.com/ArcGIS/rest/services/Canvas/World_Light_Gray_Base/MapServer" />
</esri:Map>
<esri:MapView.GraphicsOverlays>
<esri:GraphicsOverlay ID="resultsOverlay" />
</esri:MapView.GraphicsOverlays>
</esri:MapView>

<Border Background="White" BorderBrush="Black" BorderThickness="1"
HorizontalAlignment="Right" VerticalAlignment="Top"
<Border.Effect>
</Border.Effect>
<StackPanel>
<TextBlock Text="Click the 'Union Geometries' button to digitize a polygon and show the union of polygon features selected by the polygon. Resulting polygon will be shown as a blue graphic."
Width="400" TextWrapping="Wrap" />
<Button Content="Union Geometries" Margin="12,12,12,0" HorizontalAlignment="Center" Click="UnionButton_Click"/>
</StackPanel>
</Border>

<Border Background="White" BorderBrush="Black" BorderThickness="2" Margin="25"
HorizontalAlignment="Center" VerticalAlignment="Bottom"
Visibility="{Binding ElementName=MyMapView, Path=Editor.IsActive, Converter={StaticResource BooleanToVisibilityConverter}}">
<TextBlock Text="Digitize a polygon on the map." Margin="8" FontSize="14" />
</Border>
</Grid>
</UserControl>
``````
``````﻿using Esri.ArcGISRuntime.Controls;
using Esri.ArcGISRuntime.Data;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Layers;
using Esri.ArcGISRuntime.Symbology;
using System;
using System.Linq;
using System.Windows;
using System.Windows.Controls;

namespace ArcGISRuntime.Samples.Desktop
{
/// <summary>
/// Example of using the GeometryEngine.Union method to calculate the geometric union of feature geometries and a given polygon. To use this sample, the user draws a polygon over the feature polygons and the system then retrieves the union of the feature geometries and the new polygon. Resulting polygons are shown in a graphics overlay on the map.
/// </summary>
/// <title>Union</title>
/// <category>Geometry</category>
public partial class UnionGeometry : UserControl
{
private const string GDB_PATH = @"..\..\..\samples-data\maps\usa.geodatabase";

private Symbol _fillSymbol;
private FeatureLayer _statesLayer;
private GraphicsOverlay _resultGraphics;

/// <summary>Construct Union sample control</summary>
public UnionGeometry()
{
InitializeComponent();

_fillSymbol = layoutGrid.Resources["FillSymbol"] as Symbol;
_resultGraphics = MyMapView.GraphicsOverlays["resultsOverlay"];

CreateFeatureLayers();
}

// Creates a feature layer from a local .geodatabase file
private async void CreateFeatureLayers()
{
try
{
var gdb = await Geodatabase.OpenAsync(GDB_PATH);

var table = gdb.FeatureTables.First(ft => ft.Name == "US-States");
_statesLayer = new FeatureLayer() { ID = table.Name, FeatureTable = table };
MyMapView.Map.Layers.Insert(1, _statesLayer);
}
catch (Exception ex)
{
MessageBox.Show("Error creating feature layer: " + ex.Message, "Samples");
}
}

// Unions feature geometries with a user defined polygon.
private async void UnionButton_Click(object sender, RoutedEventArgs e)
{
try
{
_resultGraphics.Graphics.Clear();

// wait for user to draw a polygon
var poly = await MyMapView.Editor.RequestShapeAsync(DrawShape.Polygon);

// Take account of WrapAround
var normalizedPoly = GeometryEngine.NormalizeCentralMeridian(poly) as Polygon;

// get intersecting features from the feature layer
SpatialQueryFilter filter = new SpatialQueryFilter();
filter.Geometry = GeometryEngine.Project(normalizedPoly, _statesLayer.FeatureTable.SpatialReference);
filter.SpatialRelationship = SpatialRelationship.Intersects;
filter.MaximumRows = 52;
var stateFeatures = await _statesLayer.FeatureTable.QueryAsync(filter);

// Union the geometries and add to graphics layer
var states = stateFeatures.Select(feature => feature.Geometry);
var unionPolys = states.ToList();

var unionPoly = GeometryEngine.Union(unionPolys);
var unionGraphic = new Graphic(unionPoly, _fillSymbol);