Work with offline data

Consider taking individual layers offline as offline data if you want to construct the map or scene yourself and provide users with up-to-date information from ArcGIS Online or ArcGIS Enterprise. This topic describes how to generate and download offline data to use the following layers offline:

• Feature and annotation layers — Download a specific geographical area from a sync-enabled feature service into a mobile geodatabase. Edits can be synchronized with other users when connectivity is restored. This synchronization process allows the app to maintain an up-to-date view of the feature data.
• Tiled layers
  • Vector tiled data — ArcGIS vector tile services or vector basemaps in ArcGIS Online
  • Image tiled data — Tiled ArcGIS map services, tiled ArcGIS image services, tiled basemaps or elevation sources in ArcGIS Online

You can export and download tiled layer caches locally and access them while your device is offline. It is important to note that you cannot edit tiled layer data (vector tiled data and image tiled data). If you require updates to the tiled layer data, you must export and download them again.

Feature and annotation layers

You can take features (including annotation, related records, and attachments) offline, from a feature service, by downloading them to geodatabase feature tables within a mobile geodatabase. To do this, the feature service must be hosted on ArcGIS Enterprise 10.2.2 or later for features or from a service hosted in ArcGIS Online, provided that the feature service has been sync enabled (allow disconnected editing with synchronization).

You can use an existing feature service or create features services for your own data. To enable sync for a feature service, do the following:

• ArcGIS Online — Edit the feature service item and check the Sync check box.
• ArcGIS Enterprise — See Prepare data for offline use in the ArcGIS Server documentation.

To create the mobile geodatabase, you must do the following:

1. Generate geodatabase parameters and define the area of interest, the layers, any expression filters, and so on, if required.
2. Create the geodatabase, populate it with all the relevant features, and download it to the user's device.

Generate geodatabase parameters

When you create a mobile geodatabase, you must provide a set of parameters, described below, to define exactly which data is downloaded.

• The geographical area of interest. You typically supply the area of interest as an extent (in other words, an envelope) but point, line, and polygon (including multipart) geometries are also supported. This allows you to create more detailed areas of interest. Regardless of the geometry, any features that intersect with the supplied area of interest are extracted.
• The spatial reference of the mobile geodatabase.
• Individual layers can be managed using the AGSGenerateGeodatabaseParameters.layerOptions property:
  • Determine which layers are included in the mobile geodatabase.
  • Subset the features by providing an expression that filters features by attribute values, such as ZONE = 'COM'.
  • The synchronization model controls how edits made to the mobile geodatabase are applied back to the feature service during synchronization. The model supported is defined by the data that was used to create the sync-enabled feature service. If the data is nonversioned, the synchronization model is per layer. This is the most flexible model, allowing you to synchronize on a layer-by-layer basis, based on the layers you specify. If the data is versioned, the synchronization model is per geodatabase. This synchronizes the entire geodatabase, including all layers and tables, at once.
  • Specify whether to include feature attachments in the mobile geodatabase and whether they can be uploaded during synchronization.
  • Identify whether tables related to the layer are also included in the geodatabase.

You can obtain a default set of parameters ( AGSGenerateGeodatabaseParameters ) using the defaultGenerateGeodatabaseParametersWithExtent method on the AGSGeodatabaseSyncTask . If you provide the area of interest, the default parameters will be generated taking into account the capabilities supported by the ArcGIS feature service. You can update these default parameter values before creating the geodatabase.

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
//Instantiate the Geodatabase Sync Task
guard let url = URL(string: "http://sampleserver6.arcgisonline.com/arcgis/rest/services/Sync/SaveTheBaySync/FeatureServer") else {
    print("URL not accessible")
    return
}

geodatabaseSyncTask = AGSGeodatabaseSyncTask(url: url)
//
// define an extent within which the features are included
let extent = self.mapView.currentViewpoint(with: .boundingGeometry)?.targetGeometry as! AGSEnvelope
//
// get the default parameters for generating a geodatabase
geodatabaseSyncTask?.defaultGenerateGeodatabaseParameters(withExtent: extent, completion: {[weak self] (parameters, error) in
    if let error = error {
        print(error)
        return
    }
    guard parameters != nil else {
        print("No parameters")
        return
    }
    if let parameters = parameters {
        //
        // set some of the parameters
        parameters.syncModel = .layer
        // define the layers and features to include
        let marineLayerId = 0
        let birdsLayerId = 1
        let dolphinsOnlyWhereClause = "type = 11"
        // clear and re-create the layer options
        parameters.layerOptions.removeAll()
        parameters.layerOptions.append(AGSGenerateLayerOption(layerID: marineLayerId, whereClause: dolphinsOnlyWhereClause))
        parameters.layerOptions.append(AGSGenerateLayerOption(layerID: birdsLayerId, includeRelated: true))
        // do not return attachments
        parameters.returnAttachments = false
        //
        //
        // create the generate geodatabase job, pass in the parameters and an output path for the local geodatabase
        //...
    }
})

Create the geodatabase

Obtain a job to generate and download the geodatabase by passing the AGSGenerateGeodatabaseParameters to the AGSGeodatabaseSyncTask.generateJobWithParameters() method on the AGSGeodatabaseSyncTask class. Run the job to generate and download the geodatabase to the device.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
//Instantiate the Geodatabase Sync Task
//Get and set the parameters (as above)
//
// create the generate geodatabase job, pass in the parameters and an output path for the local geodatabase
let generateJob = self.geodatabaseSyncTask?.generateJob(with: parameters, downloadFileURL: downloadURL)

generateJob?.start(statusHandler: { (status) in
    if status == .succeeded {
        print("Job succeeded")}
    else if status == .failed {
        print("Job failed")}
    else {
        print("Sync in progress")}
}, completion: { (geodatabase, error) in
    if let error = error {
        print(error)
        return
    }
    //work with the geodatabase
}

If you generate the geodatabase using these methods, it will automatically register the geodatabase with its original service. This allows the data in the geodatabase to be synchronized with the original service. If you want to load this geodatabase onto a number of devices and allow those users to synchronize changes with the original service, you must register these individual geodatabases with the original service.

Create layers from geodatabase feature tables

Now that you have a geodatabase on your local machine or device, you'll create the relevant layer from the geodatabase feature tables.

1. Get the geodatabase from the generate geodatabase job.
2. Load the geodatabase.
   1. Create feature layers from the geodatabase feature tables.
   2. Create annotation layers from the geodatabase annotation tables.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
//load the geodatabase
geodatabase.load(completion: { (error) in
    if let error = error {
        print(error)
        return
    }
    // make a feature layer from each feature table
    for featureTable in geodatabase.geodatabaseFeatureTables {
        let featureLayer = AGSFeatureLayer(featureTable: featureTable)
        self.map.operationalLayers.add(featureLayer)
    }
    // make an annotation layer from each feature table which contains annotation
    // NOTE: annotation are stored in AGSArcGISFeatureTables rather than the more generic AGSFeatureTables
    for annotationTable in geodatabase.geodatabaseAnnotationTables {
        let annotationLayer = AGSAnnotationLayer(featureTable: annotationTable)
        self.map.operationalLayers.add(annotationLayer)
    }
})

Tiled layers

Tiled layers typically provide geographical context to your map or scene as basemaps that display beneath your data layers. Tiled layers may also provide offline elevation data for visualizing 3D terrain in a scene. You can export and download tile caches directly to your device from any tiled data source that is export enabled. Esri provides a number of vector and raster basemaps for you to export and download:

• Download vector tiled data — ArcGIS vector tile services or vector basemaps in ArcGIS Online
• Download image tiled data — Tiled ArcGIS map services, tiled ArcGIS image services, or tiled basemaps and elevation sources in ArcGIS Online

Download vector tiled data

You can take vector tiled data offline by exporting it from an ArcGIS vector tile service and downloading it as a vector tile package (.vtpk) using the AGSExportVectorTilesTask  class. The vector tile service used for this operation must support the creation of an offline vector tile cache; specifically, it must enable the  exportTiles operation. Vector tiles contain vector representations of data that can be restyled for different purposes, such as day and night viewing. You can download default styling resources along with the vector tiles and custom style resources from ArcGIS Portal items that host vector tile layers.

You have a number of workflows available to you depending on whether your vector tiled data has custom style resources, whether you want to download many custom styles that you can apply to a number of tile caches, or whether you just want to obtain the default tile cache.

To create a vector tile package (.vtpk file) and vector tile style resources, do the following:

1. Instantiate the export vector tiles task and check whether the vector tiles have custom style resources.
2. Specify the export vector tiles task parameters for a specific maximum scale and area of interest.
3. Export the vector tiles. The vector tile package is populated with vector tiles and the default style resources from the ArcGIS vector tile service.

Instantiate the export vector tiles task

Instantiate the AGSExportVectorTilesTask using a URL to the portal item that represents an ArcGIS vector tiled layer. Load the task, and upon completion, check whether the vector tiles have custom style resources by checking the hasStyleResources Boolean value.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
//initialize the export vector tiled task with a portal item that represents an ArcGIS Vector Tiled Layer
// or a URL to the ArcGIS Vector Tile service (if only default styles are required)
//
let portalItem = AGSPortalItem(portal: portal, itemID: itemID)

self.exportVectorTilesTask = AGSExportVectorTilesTask(portalItem: portalItem)
//
self.exportVectorTilesTask.load {[weak self] (error) in
    if let error = error {
        print(error.localizedDescription)
        return
    }
    guard let hasStyleResources = self?.exportVectorTilesTask.hasStyleResources else {return}
    if hasStyleResources {
        print("The vector tile package has style resources")
        // choose whether to download the tiles and the custom style resources or just the style resources alone.
    }
}

Specify the export vector tiles task parameters

To obtain a default set of parameters, call the defaultExportVectorTilesParametersWithAreaOfInterest method and provide an area of interest (polygon or envelope) and a maximum scale. When you provide the maximum scale, you must be aware that there won't be any tiles when the map is zoomed in beyond this scale. If you set the maximum scale to 0, the export will include all levels of detail in the service.

This method returns the set of default parameters, AGSExportVectorTilesParameters , required to export the vector tiles to a vector tile package. The LODs have been calculated to support the maximum scale that you specified.

1
2
3
4
5
6
7
8
9
let envelope = AGSEnvelope(xMin: -123.0, yMin: 33.5, xMax: -101.0, yMax: 48.0, spatialReference: .wgs84())
self.exportVectorTilesTask.defaultExportVectorTilesParameters(withAreaOfInterest: envelope, maxScale: self.mapView.mapScale) {[weak self] (params: AGSExportVectorTilesParameters?, error: Error?) in
    if let error = error {
        print(error)
        return
    }
    // set the export vector tile cache parameters and set them where appropriate
    self?.exportVectorTilesParameters = params
}

Export the vector tiles

Obtain a job to generate and download a vector tile package and its default style resources by passing the AGSExportVectorTilesParameters to the exportVectorTilesJobWithParameters method on the AGSExportVectorTilesTask class. You must also provide a download path to store the vector tile package and its default style resources.

Run the AGSExportVectorTilesJob to export and download the vector tile package (.vtpk).

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
//destination path for the tpk, including name
let path = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]
let destinationPath = "\(path)/myVectorTileCache.vtpk"
//
//get the job
self.exportVectorTilesJob = self.exportVectorTilesTask.exportVectorTilesJob(with: self.exportVectorTilesParameters, downloadFileURL: URL(string: destinationPath)!)
//
//run the job
self.exportVectorTilesJob.start(statusHandler: { (status: AGSJobStatus) -> Void in
    //show job status
    print(status)})
{ [weak self] (result: AnyObject?, error: Error?) -> Void in
    if let error = error {
        print(error)
        return
    }
    //check the result is a vector tile cache then add it to the map
    guard let result = result as? AGSExportVectorTilesResult else {return}
    guard let vectorTileCache = result.vectorTileCache else {return}
    let newVectorTiledLayer = AGSArcGISVectorTiledLayer(vectorTileCache: vectorTileCache)
    self?.map = AGSMap(basemap: AGSBasemap(baseLayer: newVectorTiledLayer))
}

Export the vector tiles with custom style resources

Obtain a job to generate and download a vector tile package containing tiles and associated style resources by passing the AGSExportVectorTilesParameters to the exportVectorTilesJobWithParameters method on the AGSExportVectorTilesTask class. The portal item's associated style resources will be downloaded and saved separately. You must also provide a download path to store the vector tile package and a separate download path for the style resources.

Run the job to export and download the vector tile package (.vtpk) and the style resources to the device.

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
//destination path for the vtpk, including name
let path = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]
let VTPKPath = "\(path)/myVectorTileCache.vtpk"
//
//destination path for custom style resources
let resourcesPath = "\(path)/styleResources"
//
//create the job using the parameters, the vtpk path and custom style resource path
self.exportVectorTilesJob = self.exportVectorTilesTask.exportVectorTilesJob(with: self.exportVectorTilesParameters,  vectorTileCacheDownloadFileURL: URL(string: VTPKPath)!,  itemResourceCacheDownloadDirectory: URL(string: resourcesPath)!)
//
//run the job
self.exportVectorTilesJob.start(statusHandler: { (status: AGSJobStatus) -> Void in
    //show job status
    print(status)})
{ [weak self] (result: AnyObject?, error: Error?) -> Void in
    if let error = error {
        print(error)
        return
    }
    //get the result
    guard let result = result as? AGSExportVectorTilesResult else {return}
    guard let vectorTileCache = result.vectorTileCache else {return}
    guard let itemResourceCache = result.itemResourceCache else {return}
    let newVectorTiledLayer = AGSArcGISVectorTiledLayer(vectorTileCache: vectorTileCache, itemResourceCache: itemResourceCache)
    self?.map = AGSMap(basemap: AGSBasemap(baseLayer: newVectorTiledLayer))
}

Export custom style resources

Obtain a job to download any custom style resources associated with the tasks vector tiles by passing a download path to the exportStyleResourceCacheJobWithDownloadDirectory method on the AGSExportVectorTilesTask class.

Run the job to export the style resources. Obtain the itemResourceCache property from the AGSExportVectorTilesResult class.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
//destination path for the style resources
let path = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]
let resourcesPath = "\(path)/styleResources"
//
//create the job using the custom style resource path
self.exportVectorTilesJob = self.exportVectorTilesTask.exportStyleResourceCacheJob(withDownloadDirectory:URL(string: resourcesPath)!)
//
//run the job
self.exportVectorTilesJob.start(statusHandler: { (status: AGSJobStatus) -> Void in
    //show job status
    print(status)})
{ (result: AnyObject?, error: Error?) -> Void in
    if let error = error {
        print(error)
        return
    }
    guard let result = result as? AGSExportVectorTilesResult else {return}
    guard let itemResourceCache = result.itemResourceCache else {return}
    //....
}

Download image tiled data

You can take image tiled data offline by exporting and downloading the image tiled data as a tile package (.tpk or .tpkx) using the AGSExportTileCacheTask  class. This task requires that the tiled map or image service support the creation of an offline tile cache; specifically, it must enable the exportTiles operation. This can be found at the bottom of the service's HTML page. Esri provided basemaps and elevation sources will be swapped for their export-enabled services.

To create the tile cache, do the following:

1. Generate the default export image tile cache parameters and set any of the properties.
2. Export and download the image tile cache using the methods on the AGSExportTileCacheTask .

Generate default export image tile cache parameters

Construct a default set of parameters ( AGSExportTileCacheParameters ) by passing an area of interest (polygon or envelope) along with the minimum and maximum scale thresholds to the exportTileCacheParametersWithAreaOfInterest method on the AGSExportTileCacheTask class.

This method will return a set of parameters for the area of interest and will calculate the levels of detail (LODs) required to support the minimum and maximum scale for the service's tiling scheme. You can adjust these LOD levels or remove some before you download the cache.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
// Instantiate the export task with the URL to the tiled service.
self.exportTileCacheTask = AGSExportTileCacheTask(url: self.tiledLayer.url!)
//
// Export the tile cache parameters from the tiled service.
let envelope = AGSEnvelope(xMin: -123.0, yMin: 33.5, xMax: -101.0, yMax: 48.0, spatialReference: .wgs84())
self.exportTileCacheTask.exportTileCacheParameters(withAreaOfInterest: envelope ,  minScale: 10000,  maxScale: 0)  {[weak self] (params: AGSExportTileCacheParameters?, error: Error?) in
    if let error = error {
        print(error)
        return
    }
    guard let params = params else {return}
    // obtain the export tile cache parameters
    // set these parameters and provide them to the exportTileCacheJob  // to download the tile cache to the device
    self?.exportTileCacheParameters = params
}

Export and download the image tile cache

Obtain an export and download job by passing the AGSExportTileCacheParameters to the exportTileCacheJobWithParameters method on the AGSExportTileCacheTask class. Run the job to download the tile cache into a tile package that is placed in the download path on the device.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
// Destination path for the local package (.tpkx file), including name.
let path = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]
let destinationPath = "\(path)/TerrainImageTiles.tpkx"

// Get the job.
self.exportTileCachejob = self.exportTileCacheTask.exportTileCacheJob(with: self.exportTileCacheParameters, downloadFileURL: URL(string: destinationPath)!)

// Run the job.
self.exportTileCachejob.start(statusHandler: { (status: AGSJobStatus) -> Void in
    // Report the current job status and progress.
    print(status)})
{ [weak self] (result: AnyObject?, error: Error?) -> Void in
    guard let self = self else { return }
    if let error = error {
        print(error)
        return
    }

    // When the job completes successfully, store the result (local tile cache).
    guard let tileCache = result as? AGSTileCache else {return}
    self.tileCache = tileCache
}

The tile cache from an exported basemap tile layer can be used in your map or scene:

1
2
3
4
5
// Use the tile cache to create an AGSArcGISTiledLayer.
let tiledLayer = AGSArcGISTiledLayer(tileCache: self.tileCache)
// Display the tiled layer as a basemap.
self.map = AGSMap(basemap: AGSBasemap(baseLayer: tiledLayer))
self.mapView.map = self.map

The tile cache from exported elevation data can be used as an elevation source in your scene:

1
2
3
4
5
6
let localElevationSource = AGSArcGISTiledElevationSource(tileCache: tileCache)
let elevationSurface = AGSSurface()
elevationSurface.elevationSources.append(localElevationSource)
let scene = AGSScene()
scene.baseSurface = elevationSurface
sceneView.scene = scene

When creating an offline tile cache from a tiled service, consider the following:

• The export tiles operation used to generate tile caches is only available with services hosted on ArcGIS Server 10.2.1 or later.
• Estimation of tile cache size is not available on ArcGIS Online hosted tiled services.
• The time required to create a tile cache varies depending on the extent requested, the number of levels requested, the network connection speed, and so on. Use the estimateTileCacheSizeJobWithParameters method on the  AGSExportTileCacheTask  class, which returns an  EstimateTileCacheSizeJob  to get the approximate size of a tile cache for a specific set of parameters. Try generating a smaller tile cache to get an idea of how long caching will take when planning a large offline data capture event.
• There is a limit to the number of tiles you can generate in a single request. When generating a tile cache from an ArcGIS Online basemap, there is a limit of 100,000 tiles per request. Read more on this in the ArcGIS REST API documentation. Organizations that use their own ArcGIS Server to host an offline tile cache can configure the server's maxExportTilesCount via the administrator account to change the default limit of 100,000 tiles.