# Nearest vertex

This code sample is available for these platforms:

Find the closest vertex and coordinate of a geometry to a point.

## Use case

Determine the shortest distance between a location and the boundary of an area. For example, developers can snap imprecise user clicks to a geometry if the tap is within a certain distance of the geometry.

## How to use the sample

Tap anywhere on the map. An orange cross will show at that location. A blue circle will show the polygon's nearest vertex to the point that was clicked. A red diamond will appear at the coordinate on the geometry that is nearest to the point that was clicked. If clicked inside the geometry, the red and orange markers will overlap. The information box showing distance between the clicked point and the nearest vertex/coordinate will be updated with every new location clicked.

## How it works

1. Get a `Geometry` and a `Point` to check the nearest vertex against.
2. Call `GeometryEngine.NearestVertex(inputGeometry, point)`.
3. Use the returned `ProximityResult` to get the `Point` representing the polygon vertex, and to determine the distance between that vertex and the clicked point.
4. Call `GeometryEngine.NearestCoordinate(inputGeometry, point)`.
5. Use the returned `ProximityResult` to get the `Point` representing the coordinate on the polygon, and to determine the distance between that coordinate and the clicked point.

## Relevant API

• GeometryEngine
• ProximityResult

## Tags

analysis, coordinate, geometry, nearest, proximity, vertex

## Sample Code

``````<?xml version="1.0" encoding="utf-8" ?>
<ContentPage
x:Class="ArcGISRuntime.Samples.NearestVertex.NearestVertex"
xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:forms="clr-namespace:Esri.ArcGISRuntime.Xamarin.Forms;assembly=Esri.ArcGISRuntime.Xamarin.Forms">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Label
x:Name="ResultsLabel"
Grid.Row="0"
HorizontalTextAlignment="Center"
TextColor="Red">
Tap to see the nearest vertex and point.
</Label>
<forms:MapView x:Name="MyMapView" Grid.Row="1" />
</Grid>
</ContentPage>``````
``````// Copyright 2020 Esri.
//
//
// 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 Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.UI;
using Colors = System.Drawing.Color;

namespace ArcGISRuntime.Samples.NearestVertex
{
[ArcGISRuntime.Samples.Shared.Attributes.Sample(
name: "Nearest vertex",
category: "Geometry",
description: "Find the closest vertex and coordinate of a geometry to a point.",
instructions: "Tap anywhere on the map. An orange cross will show at that location. A blue circle will show the polygon's nearest vertex to the point that was clicked. A red diamond will appear at the coordinate on the geometry that is nearest to the point that was clicked. If clicked inside the geometry, the red and orange markers will overlap. The information box showing distance between the clicked point and the nearest vertex/coordinate will be updated with every new location clicked.",
tags: new[] { "analysis", "coordinate", "geometry", "nearest", "proximity", "vertex" })]
public partial class NearestVertex
{
// Hold references to the graphics overlay and the polygon graphic
private GraphicsOverlay _graphicsOverlay;
private Graphic _polygonGraphic;

// Hold references to the graphics for the user and results points
private Graphic _tappedLocationGraphic;
private Graphic _nearestVertexGraphic;
private Graphic _nearestCoordinateGraphic;

public NearestVertex()
{
InitializeComponent();

Initialize();
}

private void Initialize()
{
// Configure the basemap
MyMapView.Map = new Map(Basemap.CreateTopographic());

// Create the graphics overlay and set the selection color
_graphicsOverlay = new GraphicsOverlay();

// Add the overlay to the MapView

// Create the point collection that defines the polygon
PointCollection polygonPoints = new PointCollection(SpatialReferences.WebMercator)
{
new MapPoint(-5991501.677830, 5599295.131468),
new MapPoint(-6928550.398185, 2087936.739807),
new MapPoint(-3149463.800709, 1840803.011362),
new MapPoint(-1563689.043184, 3714900.452072),
new MapPoint(-3180355.516764, 5619889.608838)
};

// Create the polygon
Polygon polygonGeometry = new Polygon(polygonPoints);

// Define and apply the symbology
SimpleLineSymbol polygonOutlineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, Colors.Green, 2);
SimpleFillSymbol polygonFillSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle.ForwardDiagonal, Colors.Green, polygonOutlineSymbol);

// Create the graphic and add it to the graphics overlay
_polygonGraphic = new Graphic(polygonGeometry, polygonFillSymbol);

// Create the graphics and symbology for the tapped point, the nearest vertex, and the nearest coordinate
SimpleMarkerSymbol tappedLocationSymbol = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle.X, Colors.Orange, 15);
SimpleMarkerSymbol nearestCoordinateSymbol = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle.Diamond, Colors.Red, 10);
SimpleMarkerSymbol nearestVertexSymbol = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle.Circle, Colors.Blue, 15);
_nearestCoordinateGraphic = new Graphic { Symbol = nearestCoordinateSymbol };
_tappedLocationGraphic = new Graphic { Symbol = tappedLocationSymbol };
_nearestVertexGraphic = new Graphic { Symbol = nearestVertexSymbol };

// Listen for taps; the spatial relationships will be updated in the handler
MyMapView.GeoViewTapped += MapViewTapped;

// Center the map on the polygon
MyMapView.SetViewpointCenterAsync(polygonGeometry.Extent.GetCenter(), 200000000);
}

private void MapViewTapped(object sender, Esri.ArcGISRuntime.Xamarin.Forms.GeoViewInputEventArgs geoViewInputEventArgs)
{
// Get the tapped location
MapPoint tappedLocation = (MapPoint)GeometryEngine.NormalizeCentralMeridian(geoViewInputEventArgs.Location);

// Show the tapped location
_tappedLocationGraphic.Geometry = tappedLocation;

// Get the nearest vertex in the polygon
ProximityResult nearestVertexResult = GeometryEngine.NearestVertex(_polygonGraphic.Geometry, tappedLocation);

// Get the nearest coordinate in the polygon
ProximityResult nearestCoordinateResult =
GeometryEngine.NearestCoordinate(_polygonGraphic.Geometry, tappedLocation);

// Get the distance to the nearest vertex in the polygon
int distanceVertex = (int)(nearestVertexResult.Distance / 1000);

// Get the distance to the nearest coordinate in the polygon
int distanceCoordinate = (int)(nearestCoordinateResult.Distance / 1000);

// Show the nearest vertex in blue
_nearestVertexGraphic.Geometry = nearestVertexResult.Coordinate;

// Show the nearest coordinate in red
_nearestCoordinateGraphic.Geometry = nearestCoordinateResult.Coordinate;

// Show the distances in the UI
ResultsLabel.Text = \$"Vertex dist: {distanceVertex} km, Point dist: {distanceCoordinate} km";
}
}
}``````