Buffer

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Create a buffer around a map point and display the results as a Graphic

Image of Buffer

Use case

Creating buffers is a core concept in GIS proximity analysis that allows you to visualize and locate geographic features contained within a polygon. For example, suppose you wanted to visualize areas of your city where alcohol sales are prohibited because they are within 500 meters of a school. The first step in this proximity analysis would be to generate 500 meter buffer polygons around all schools in the city. Any such businesses you find inside one of the resulting polygons are violating the law.

How to use the sample

  1. Tap on the map.
  2. A planar and a geodesic buffer will be created at the tap location using the distance (miles) specified in the text box.
  3. Continue tapping to create additional buffers. Notice that buffers closer to the equator appear similar in size. As you move north or south from the equator, however, the geodesic polygons become much larger. Geodesic polygons are in fact a better representation of the true shape and size of the buffer.
  4. Tap Clear to remove all buffers and start again.

How it works

  1. The MapPoint for a tap on the display is captured.
  2. The static method GeometryEngine.Buffer is called to create a planar buffer polygon from the map location and distance.
  3. Another static method, GeometryEngine.BufferGeodetic is called to create a geodesic buffer polygon using the same inputs.
  4. The polygon results (and tap location) are displayed in the map view with different symbols in order to highlight the difference between the buffer techniques due to the spatial reference used in the planar calculation.

Relevant API

  • GeometryEngine.Buffer
  • GeometryEngine.BufferGeodetic
  • GraphicsOverlay

Additional information

Buffers can be generated as either planar (flat - coordinate space of the map's spatial reference) or geodesic (technique that considers the curved shape of the Earth's surface, which is generally a more accurate representation). In general, distortion in the map increases as you move away from the standard parallels of the spatial reference's projection. This map is in Web Mercator so areas near the equator are the most accurate. As you move the buffer location north or south from that line, you'll see a greater difference in the polygon size and shape. Planar operations are generally faster, but performance improvement may only be noticeable for large operations (buffering a great number or complex geometry).

For more information about using buffer analysis, see the topic How Buffer (Analysis) works in the ArcGIS Pro documentation.

Tags

analysis, buffer, euclidean, geodesic, geometry, planar

Sample Code

Buffer.cs
                                                                                                                                                                                                                                                                                                                                                           
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// Copyright 2018 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 System;
using CoreGraphics;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.UI;
using Esri.ArcGISRuntime.UI.Controls;
using Foundation;
using UIKit;
using Colors = System.Drawing.Color;

namespace ArcGISRuntime.Samples.Buffer
{
    [Register("Buffer")]
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        name: "Buffer",
        category: "Geometry",
        description: "Create a buffer around a map point and display the results as a `Graphic`",
        instructions: "1. Tap on the map.",
        tags: new[] { "analysis", "buffer", "euclidean", "geodesic", "geometry", "planar" })]
    public class Buffer : UIViewController
    {
        // Hold references to UI controls.
        private MapView _myMapView;
        private UITextField _bufferDistanceMilesTextField;
        private UIView _geodesicSwatchSwatch;
        private UIView _planarSwatchSwatch;
        private UIButton _clearBuffersButton;

        public Buffer()
        {
            Title = "Buffer";
        }

        private void Initialize()
        {
            // Create a map with a topographic basemap and add it to the map view.
            _myMapView.Map = new Map(BasemapStyle.ArcGISTopographic);

            // Create a fill symbol for geodesic buffer polygons.
            Colors geodesicBufferColor = Colors.FromArgb(120, 255, 0, 0);
            SimpleLineSymbol geodesicOutlineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, geodesicBufferColor, 2);
            SimpleFillSymbol geodesicBufferFillSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle.Solid, geodesicBufferColor, geodesicOutlineSymbol);

            // Create a fill symbol for planar buffer polygons.
            Colors planarBufferColor = Colors.FromArgb(120, 0, 0, 255);
            SimpleLineSymbol planarOutlineSymbol = new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, planarBufferColor, 2);
            SimpleFillSymbol planarBufferFillSymbol = new SimpleFillSymbol(SimpleFillSymbolStyle.Solid, planarBufferColor, planarOutlineSymbol);

            // Create a marker symbol for tap locations.
            SimpleMarkerSymbol tapSymbol = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle.Cross, System.Drawing.Color.White, 14);

            // Create a graphics overlay to display geodesic polygons, set its renderer and add it to the map view.
            GraphicsOverlay geodesicPolysOverlay = new GraphicsOverlay
            {
                Id = "GeodesicPolys",
                Renderer = new SimpleRenderer(geodesicBufferFillSymbol)
            };
            _myMapView.GraphicsOverlays.Add(geodesicPolysOverlay);

            // Create a graphics overlay to display planar polygons, set its renderer and add it to the map view.
            GraphicsOverlay planarPolysOverlay = new GraphicsOverlay
            {
                Id = "PlanarPolys",
                Renderer = new SimpleRenderer(planarBufferFillSymbol)
            };
            _myMapView.GraphicsOverlays.Add(planarPolysOverlay);

            // Create a graphics overlay to display tap locations for buffers, set its renderer and add it to the map view.
            GraphicsOverlay tapLocationsOverlay = new GraphicsOverlay
            {
                Id = "TapPoints",
                Renderer = new SimpleRenderer(tapSymbol)
            };
            _myMapView.GraphicsOverlays.Add(tapLocationsOverlay);

            // Show the colors for each type of buffer in the UI.
            ShowBufferSwatches(planarBufferColor, geodesicBufferColor);
        }

        private void MyMapView_GeoViewTapped(object sender, GeoViewInputEventArgs e)
        {
            // Hide keyboard if present.
            _bufferDistanceMilesTextField.ResignFirstResponder();

            try
            {
                // Get the location tapped by the user (a map point in the WebMercator projected coordinate system).
                MapPoint userTapPoint = e.Location;

                // Get the buffer distance (miles) entered in the text box.
                double bufferInMiles = Convert.ToDouble(_bufferDistanceMilesTextField.Text);

                // Call a helper method to convert the input distance to meters.
                double bufferInMeters = LinearUnits.Miles.ToMeters(bufferInMiles);

                // Create a planar buffer graphic around the input location at the specified distance.
                Geometry bufferGeometryPlanar = GeometryEngine.Buffer(userTapPoint, bufferInMeters);
                Graphic planarBufferGraphic = new Graphic(bufferGeometryPlanar);

                // Create a geodesic buffer graphic using the same location and distance.
                Geometry bufferGeometryGeodesic = GeometryEngine.BufferGeodetic(userTapPoint, bufferInMeters, LinearUnits.Meters, double.NaN, GeodeticCurveType.Geodesic);
                Graphic geodesicBufferGraphic = new Graphic(bufferGeometryGeodesic);

                // Create a graphic for the user tap location.
                Graphic locationGraphic = new Graphic(userTapPoint);

                // Get the graphics overlays.
                GraphicsOverlay planarBufferGraphicsOverlay = _myMapView.GraphicsOverlays["PlanarPolys"];
                GraphicsOverlay geodesicBufferGraphicsOverlay = _myMapView.GraphicsOverlays["GeodesicPolys"];
                GraphicsOverlay tapPointGraphicsOverlay = _myMapView.GraphicsOverlays["TapPoints"];

                // Add the buffer polygons and tap location graphics to the appropriate graphic overlays.
                planarBufferGraphicsOverlay.Graphics.Add(planarBufferGraphic);
                geodesicBufferGraphicsOverlay.Graphics.Add(geodesicBufferGraphic);
                tapPointGraphicsOverlay.Graphics.Add(locationGraphic);
            }
            catch (Exception ex)
            {
                // Display an error message if there is a problem generating the buffers.
                UIAlertController alertController = UIAlertController.Create("Error creating buffers", ex.Message, UIAlertControllerStyle.Alert);
                alertController.AddAction(UIAlertAction.Create("OK", UIAlertActionStyle.Default, null));
                PresentViewController(alertController, true, null);
            }
        }

        private void ShowBufferSwatches(Colors planarBufferColor, Colors geodesicBufferColor)
        {
            // Create UIKit.UIColors to represent the System.Drawing.Colors used for the buffers.
            UIColor planarLabelColor = UIColor.FromRGBA(planarBufferColor.R,
                planarBufferColor.G,
                planarBufferColor.B,
                planarBufferColor.A);
            UIColor geodesicLabelColor = UIColor.FromRGBA(geodesicBufferColor.R,
                geodesicBufferColor.G,
                geodesicBufferColor.B,
                geodesicBufferColor.A);

            // Show buffer symbol colors in the UI by setting the appropriate text view fill color.
            _planarSwatchSwatch.BackgroundColor = planarLabelColor;
            _geodesicSwatchSwatch.BackgroundColor = geodesicLabelColor;
        }

        private void ClearBuffersButton_TouchUpInside(object sender, EventArgs e)
        {
            // Hide keyboard if present.
            _bufferDistanceMilesTextField.ResignFirstResponder();

            // Clear the buffer and point graphics.
            foreach (GraphicsOverlay ov in _myMapView.GraphicsOverlays)
            {
                ov.Graphics.Clear();
            }
        }

        public override void ViewDidLoad()
        {
            base.ViewDidLoad();
            Initialize();
        }

        public override void LoadView()
        {
            // Create the views.
            View = new UIView {BackgroundColor = ApplicationTheme.BackgroundColor};

            _myMapView = new MapView();
            _myMapView.TranslatesAutoresizingMaskIntoConstraints = false;

            UILabel helpLabel = new UILabel
            {
                Text = "Tap the map to create planar and geodesic buffers.",
                TextAlignment = UITextAlignment.Center,
                AdjustsFontSizeToFitWidth = true,
                Lines = 1,
                TranslatesAutoresizingMaskIntoConstraints = false
            };

            UIView formArea = new UIView {BackgroundColor = ApplicationTheme.BackgroundColor};
            formArea.TranslatesAutoresizingMaskIntoConstraints = false;

            UILabel bufferInputLabel = new UILabel
            {
                Text = "Distance (miles):",
                TextAlignment = UITextAlignment.Right,
                TranslatesAutoresizingMaskIntoConstraints = false
            };

            _bufferDistanceMilesTextField = new UITextField
            {
                BackgroundColor = UIColor.LightGray,
                KeyboardType = UIKeyboardType.NumberPad,
                Text = "1000",
                TextAlignment = UITextAlignment.Right,
                TranslatesAutoresizingMaskIntoConstraints = false
            };
            _bufferDistanceMilesTextField.Layer.CornerRadius = 5;

            // Add padding within the field.
            _bufferDistanceMilesTextField.RightView = new UIView(new CGRect(0, 0, 5, 20)); // 5 is amount of left padding.
            _bufferDistanceMilesTextField.RightViewMode = UITextFieldViewMode.Always;

            UIStackView legendView = new UIStackView();
            legendView.TranslatesAutoresizingMaskIntoConstraints = false;
            legendView.Axis = UILayoutConstraintAxis.Horizontal;
            legendView.Alignment = UIStackViewAlignment.Center;
            legendView.Spacing = 8;

            _geodesicSwatchSwatch = new UIView();
            _geodesicSwatchSwatch.TranslatesAutoresizingMaskIntoConstraints = false;
            _geodesicSwatchSwatch.BackgroundColor = UIColor.Red;
            _geodesicSwatchSwatch.WidthAnchor.ConstraintEqualTo(16).Active = true;
            _geodesicSwatchSwatch.HeightAnchor.ConstraintEqualTo(16).Active = true;
            _geodesicSwatchSwatch.ClipsToBounds = true;
            _geodesicSwatchSwatch.Layer.CornerRadius = 8;
            legendView.AddArrangedSubview(_geodesicSwatchSwatch);

            UILabel geodesicSwatchLabel = new UILabel
            {
                Text = "Geodesic buffers",
                TextColor = UIColor.Red,
                TranslatesAutoresizingMaskIntoConstraints = false
            };
            legendView.AddArrangedSubview(geodesicSwatchLabel);

            UIView spacer = new UIView();
            spacer.TranslatesAutoresizingMaskIntoConstraints = false;
            spacer.SetContentCompressionResistancePriority((float) UILayoutPriority.DefaultLow, UILayoutConstraintAxis.Horizontal);
            legendView.AddArrangedSubview(spacer);

            _planarSwatchSwatch = new UIView();
            _planarSwatchSwatch.BackgroundColor = UIColor.Blue;
            _planarSwatchSwatch.TranslatesAutoresizingMaskIntoConstraints = false;
            _planarSwatchSwatch.WidthAnchor.ConstraintEqualTo(16).Active = true;
            _planarSwatchSwatch.HeightAnchor.ConstraintEqualTo(16).Active = true;
            _planarSwatchSwatch.ClipsToBounds = true;
            _planarSwatchSwatch.Layer.CornerRadius = 8;
            legendView.AddArrangedSubview(_planarSwatchSwatch);

            UILabel planarSwatchLabel = new UILabel
            {
                Text = "Planar buffers",
                TextColor = UIColor.Blue,
                TranslatesAutoresizingMaskIntoConstraints = false
            };
            legendView.AddArrangedSubview(planarSwatchLabel);

            _clearBuffersButton = new UIButton
            {
                ClipsToBounds = true,
                BackgroundColor = View.TintColor
            };
            _clearBuffersButton.SetTitle("Clear", UIControlState.Normal);
            _clearBuffersButton.SetTitleColor(ApplicationTheme.ForegroundColor, UIControlState.Normal);
            _clearBuffersButton.Layer.CornerRadius = 5;
            _clearBuffersButton.TranslatesAutoresizingMaskIntoConstraints = false;

            // Add the views.
            View.AddSubviews(_myMapView,
                formArea,
                helpLabel,
                bufferInputLabel,
                _bufferDistanceMilesTextField,
                legendView,
                _clearBuffersButton);

            // Lay out the views.
            // TODO: consider replacing with UIStackView-based layout.
            nfloat margin = 8;
            nfloat controlHeight = 4 * margin;

            NSLayoutConstraint.ActivateConstraints(new[]
            {
                formArea.TopAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TopAnchor),
                formArea.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                formArea.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),
                formArea.HeightAnchor.ConstraintEqualTo((3 * margin) + (2 * controlHeight)),

                legendView.LeadingAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.LeadingAnchor, 8),
                legendView.TrailingAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TrailingAnchor, -8),
                legendView.TopAnchor.ConstraintEqualTo(formArea.BottomAnchor),
                legendView.HeightAnchor.ConstraintEqualTo(24),

                _myMapView.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                _myMapView.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),
                _myMapView.TopAnchor.ConstraintEqualTo(legendView.BottomAnchor),
                _myMapView.BottomAnchor.ConstraintEqualTo(View.BottomAnchor),

                helpLabel.TopAnchor.ConstraintEqualTo(formArea.TopAnchor, margin),
                helpLabel.LeadingAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.LeadingAnchor),
                helpLabel.TrailingAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TrailingAnchor),
                helpLabel.HeightAnchor.ConstraintEqualTo(controlHeight),

                bufferInputLabel.TopAnchor.ConstraintEqualTo(helpLabel.BottomAnchor, margin),
                bufferInputLabel.LeadingAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.LeadingAnchor, margin),
                bufferInputLabel.TrailingAnchor.ConstraintEqualTo(formArea.CenterXAnchor, -margin),
                bufferInputLabel.HeightAnchor.ConstraintEqualTo(controlHeight),

                _bufferDistanceMilesTextField.TopAnchor.ConstraintEqualTo(bufferInputLabel.TopAnchor),
                _bufferDistanceMilesTextField.LeadingAnchor.ConstraintEqualTo(formArea.CenterXAnchor, margin),
                _bufferDistanceMilesTextField.TrailingAnchor.ConstraintEqualTo(_clearBuffersButton.LeadingAnchor, -margin),
                _bufferDistanceMilesTextField.HeightAnchor.ConstraintEqualTo(controlHeight),

                _clearBuffersButton.TopAnchor.ConstraintEqualTo(_bufferDistanceMilesTextField.TopAnchor),
                _clearBuffersButton.WidthAnchor.ConstraintEqualTo(100),
                _clearBuffersButton.TrailingAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TrailingAnchor, -margin),
                _clearBuffersButton.HeightAnchor.ConstraintEqualTo(controlHeight)
            });
        }

        private bool HandleTextField(UITextField textField)
        {
            // This method allows pressing 'return' to dismiss the software keyboard.
            textField.ResignFirstResponder();
            return true;
        }

        public override void ViewWillAppear(bool animated)
        {
            base.ViewWillAppear(animated);

            // Subscribe to events.
            _myMapView.GeoViewTapped += MyMapView_GeoViewTapped;
            _clearBuffersButton.TouchUpInside += ClearBuffersButton_TouchUpInside;
            _bufferDistanceMilesTextField.ShouldReturn += HandleTextField;
        }

        public override void ViewDidDisappear(bool animated)
        {
            base.ViewDidDisappear(animated);

            // Unsubscribe from events, per best practice.
            _myMapView.GeoViewTapped -= MyMapView_GeoViewTapped;
            _bufferDistanceMilesTextField.ShouldReturn -= HandleTextField;
            _clearBuffersButton.TouchUpInside -= ClearBuffersButton_TouchUpInside;
        }
    }
}

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