Generate offline map with local basemap

View on GitHub

Use the OfflineMapTask to take a web map offline, but instead of downloading an online basemap, use one which is already on the device.

Image of generate offline map with local basemap

Use case

There are a number of use-cases where you may wish to use a basemap which is already on the device, rather than downloading:

  • You want to limit the total download size.
  • You want to be able to share a single set of basemap files between many offline maps.
  • You want to use a custom basemap (for example authored in ArcGIS Pro) which is not available online.
  • You do not wish to sign into ArcGIS.com in order to download Esri basemaps.

The author of a web map can support the use of basemaps which are already on a device by configuring the web map to specify the name of a suitable basemap file. This could be a basemap which:

  • Has been authored in ArcGIS Pro to make use of your organizations custom data.
  • Is available as a portal item which can be downloaded once and re-used many times.

How to use the sample

When the sample loads, tap the "Generate Offline Map" button. You will be prompted to choose whether you wish to download the online basemap or use the local "naperville_imagery.tpkx" basemap which is already on the device.

If you choose to download the online basemap, the offline map will be generated with the same (topographic) basemap as the online web map. To download the Esri basemap, you may be prompted to sign in to ArcGIS.com.

If you choose to use the basemap from the device, the offline map will be generated with the local imagery basemap. The download will be quicker since no tiles are exported or downloaded.

Since the application is not exporting online ArcGIS Online basemaps you will not need to log-in.

How it works

  1. Create a PortalItem object using a web map's ID.
  2. Initialize an OfflineMapTask object using the map created with the portal item.
  3. Get the default parameters for the task by calling OfflineMapTask.makeDefaultGenerateOfflineMapParameters(areaOfInterest:) with the selected extent.
  4. Check the GenerateOfflineMapParameters.referenceBasemapFilename property. The author of an online web map can configure this setting to indicate the name of a suitable basemap. In this example, the application checks the app bundle for the suggested "naperville_imagery.tpkx" file - and if found, asks the user whether they wish to use this instead of downloading.
  5. Set the GenerateOfflineMapParameters.referenceBasemapDirectoryURL to the absolute path of the directory which contains the .tpkx file, if the user chooses to use the basemap on the device.
  6. Create an GenerateOfflineMapJob by calling OfflineMapTask.makeGenerateOfflineMapJob(parameters:downloadDirectory:) passing the parameters and the download location for the offline map.
  7. Start the GenerateOfflineMapJob. It will check whether GenerateOfflineMapParameters.referenceBasemapDirectoryURL has been set. If this property is set, no online basemap will be downloaded and instead, the mobile map will be created with a reference to the .tpkx on the device.

Relevant API

  • GenerateOfflineMapJob
  • GenerateOfflineMapParameters
  • GenerateOfflineMapResult
  • OfflineMapTask

Offline data

This sample uses naperville_imagery.tpkx TileCache. It is downloaded from ArcGIS Online automatically.

Tags

basemap, download, local, offline, save, web map

Sample Code

GenerateOfflineMapWithLocalBasemapView.swift
Use dark colors for code blocksCopy
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
// Copyright 2024 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
//
//   https://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.

import ArcGIS
import SwiftUI

struct GenerateOfflineMapWithLocalBasemapView: View {
    /// A Boolean value indicating whether the job is generating an offline map.
    @State private var isGeneratingOfflineMap = false

    /// A Boolean value indicating when the basemap choice dialog is presented.
    @State private var basemapChoiceIsPresented = false

    /// A Boolean value indicating whether the job is cancelling.
    @State private var isCancellingJob = false

    /// The error shown in the error alert.
    @State private var error: Error?

    /// The title to show in the confirmation dialog.
    private let basemapChoiceTitle: String = {
        let displayName = Bundle.main.object(forInfoDictionaryKey: "CFBundleName") as! String
        return String(format: "“%@” has a local imagery basemap that can be used in the map. Would you like to use the local or the online basemap?", displayName)
    }()

    /// The view model for this sample.
    @StateObject private var model = Model()

    var body: some View {
        GeometryReader { geometry in
            MapViewReader { mapView in
                MapView(map: model.offlineMap ?? model.onlineMap)
                    .interactionModes(isGeneratingOfflineMap ? [] : [.pan, .zoom])
                    .errorAlert(presentingError: $error)
                    .task {
                        do {
                            try await model.initializeOfflineMapTask()
                        } catch {
                            self.error = error
                        }
                    }
                    .onDisappear {
                        Task { await model.cancelJob() }
                    }
                    .overlay {
                        Rectangle()
                            .stroke(.red, lineWidth: 2)
                            .padding(EdgeInsets(top: 20, leading: 20, bottom: 44, trailing: 20))
                            .opacity(model.offlineMap == nil ? 1 : 0)
                    }
                    .overlay {
                        if isGeneratingOfflineMap,
                           let progress = model.generateOfflineMapJob?.progress {
                            VStack(spacing: 16) {
                                ProgressView(progress)
                                    .progressViewStyle(.linear)
                                    .frame(maxWidth: 200)

                                Button("Cancel") {
                                    isCancellingJob = true
                                }
                                .disabled(isCancellingJob)
                                .task(id: isCancellingJob) {
                                    guard isCancellingJob else { return }
                                    // Cancels the job.
                                    await model.cancelJob()
                                    // Sets cancelling the job and generating an
                                    // offline map to false.
                                    isCancellingJob = false
                                    isGeneratingOfflineMap = false
                                }
                            }
                            .padding()
                            .background(.regularMaterial)
                            .clipShape(RoundedRectangle(cornerRadius: 15))
                            .shadow(radius: 3)
                        }
                    }
                    .overlay(alignment: .top) {
                        Text("Offline map generated.")
                            .frame(maxWidth: .infinity, alignment: .center)
                            .padding(8)
                            .background(.thinMaterial, ignoresSafeAreaEdges: .horizontal)
                            .opacity(model.offlineMap != nil ? 1 : 0)
                    }
                    .toolbar {
                        ToolbarItem(placement: .bottomBar) {
                            Button("Generate Offline Map") {
                                if model.canUseLocalBasemap {
                                    basemapChoiceIsPresented = true
                                } else {
                                    isGeneratingOfflineMap = true
                                }
                            }
                            .disabled(model.isGenerateDisabled || isGeneratingOfflineMap)
                            .confirmationDialog(
                                basemapChoiceTitle,
                                isPresented: $basemapChoiceIsPresented,
                                titleVisibility: .visible
                            ) {
                                Button("Use Local Basemap") {
                                    model.usesLocalBasemap = true
                                    isGeneratingOfflineMap = true
                                }
                                Button("Use Online Basemap") {
                                    model.usesLocalBasemap = false
                                    isGeneratingOfflineMap = true
                                }
                            }
                            .task(id: isGeneratingOfflineMap) {
                                guard isGeneratingOfflineMap else { return }

                                // Creates a rectangle from the area of interest.
                                let viewRect = geometry.frame(in: .local).inset(
                                    by: UIEdgeInsets(
                                        top: 20,
                                        left: geometry.safeAreaInsets.leading + 20,
                                        bottom: 44,
                                        right: -geometry.safeAreaInsets.trailing + 20
                                    )
                                )

                                // Creates an envelope from the rectangle.
                                guard let extent = mapView.envelope(fromViewRect: viewRect) else { return }

                                do {
                                    // Generates an offline map.
                                    try await model.generateOfflineMap(extent: extent)
                                } catch {
                                    self.error = error
                                }

                                // Sets generating an offline map to false.
                                isGeneratingOfflineMap = false
                            }
                        }
                    }
            }
        }
    }
}

private extension GenerateOfflineMapWithLocalBasemapView {
    /// The model used to store the geo model and other expensive objects
    /// used in this view.
    @MainActor
    class Model: ObservableObject {
        /// The offline map that is generated.
        @Published private(set) var offlineMap: Map!

        /// A Boolean value indicating whether the generate button is disabled.
        @Published private(set) var isGenerateDisabled = true

        /// A Boolean value indicating if the local basemap is available to be used.
        let canUseLocalBasemap = FileManager.default.fileExists(atPath: URL.napervilleImageryBasemap.path())

        /// A Boolean value indicating whether the offline map uses the local or online basemap.
        var usesLocalBasemap = false

        /// The generate offline map job.
        @Published private(set) var generateOfflineMapJob: GenerateOfflineMapJob!

        /// The offline map task.
        private var offlineMapTask: OfflineMapTask!

        /// A URL to a temporary directory where the offline map files are stored.
        private let temporaryDirectory = createTemporaryDirectory()

        /// The online map that is loaded from a portal item.
        let onlineMap: Map = {
            // A portal item displaying the Naperville, IL water network.
            let napervillePortalItem = PortalItem(
                portal: .arcGISOnline(connection: .anonymous),
                id: .napervilleWaterNetwork
            )

            // Creates map with portal item.
            let map = Map(item: napervillePortalItem)

            // Sets the min scale to avoid requesting a huge download.
            map.minScale = 1e4

            return map
        }()

        deinit {
            // Removes the temporary directory.
            try? FileManager.default.removeItem(at: temporaryDirectory)
        }

        /// Initializes the offline map task.
        func initializeOfflineMapTask() async throws {
            // Waits for the online map to load.
            try await onlineMap.load()
            offlineMapTask = OfflineMapTask(onlineMap: onlineMap)
            isGenerateDisabled = false
        }

        /// Creates the generate offline map parameters.
        /// - Parameter areaOfInterest: The area of interest to create the parameters for.
        /// - Returns: A `GenerateOfflineMapParameters` if there are no errors.
        private func makeGenerateOfflineMapParameters(areaOfInterest: Envelope) async throws -> GenerateOfflineMapParameters {
            // Returns the default parameters for the offline map task.
            return try await offlineMapTask.makeDefaultGenerateOfflineMapParameters(areaOfInterest: areaOfInterest)
        }

        /// Generates the offline map.
        /// - Parameter extent: The area of interest's envelope to generate an offline map for.
        func generateOfflineMap(extent: Envelope) async throws {
            // Disables the generate offline map button.
            isGenerateDisabled = true

            // Creates the default parameters for the offline map task.
            let parameters = try await makeGenerateOfflineMapParameters(areaOfInterest: extent)
            parameters.includesBasemap = true
            if canUseLocalBasemap && usesLocalBasemap {
                parameters.referenceBasemapDirectoryURL = .napervilleImageryBasemap.deletingLastPathComponent()
                parameters.referenceBasemapFilename = URL.napervilleImageryBasemap.lastPathComponent
            }

            // Creates the generate offline map job based on the parameters.
            generateOfflineMapJob = offlineMapTask.makeGenerateOfflineMapJob(
                parameters: parameters,
                downloadDirectory: temporaryDirectory
            )

            // Starts the job.
            generateOfflineMapJob.start()

            defer {
                generateOfflineMapJob = nil
                isGenerateDisabled = offlineMap != nil
            }

            // Awaits the output of the job.
            let output = try await generateOfflineMapJob.output
            // Sets the offline map to the output's offline map.
            offlineMap = output.offlineMap
            // Sets the initial viewpoint of the offline map.
            offlineMap.initialViewpoint = Viewpoint(boundingGeometry: extent.expanded(by: 0.8))
        }

        /// Cancels the generate offline map job.
        func cancelJob() async {
            // Cancels the generate offline map job.
            await generateOfflineMapJob?.cancel()
            generateOfflineMapJob = nil
        }

        /// Creates a temporary directory.
        private static func createTemporaryDirectory() -> URL {
            // swiftlint:disable:next force_try
            try! FileManager.default.url(
                for: .itemReplacementDirectory,
                in: .userDomainMask,
                appropriateFor: FileManager.default.temporaryDirectory,
                create: true
            )
        }
    }
}

private extension Envelope {
    /// Expands the envelope by a given factor.
    /// - Parameter factor: The amount to expand the envelope by.
    /// - Returns: An envelope expanded by the specified factor.
    func expanded(by factor: Double) -> Envelope {
        let builder = EnvelopeBuilder(envelope: self)
        builder.expand(by: factor)
        return builder.toGeometry()
    }
}

private extension URL {
    /// A URL to the local Naperville imagery basemap.
    static var napervilleImageryBasemap: URL {
        Bundle.main.url(forResource: "naperville_imagery", withExtension: "tpkx")!
    }
}

private extension PortalItem.ID {
    /// The portal item ID of the Naperville water network web map to be displayed on the map.
    static var napervilleWaterNetwork: Self { Self("acc027394bc84c2fb04d1ed317aac674")! }
}

#Preview {
    NavigationStack {
        GenerateOfflineMapWithLocalBasemapView()
    }
}

Your browser is no longer supported. Please upgrade your browser for the best experience. See our browser deprecation post for more details.