Types of layers

There are several types of layers and each type has different capabilities and behaves differently. Layers represent geographic features such as points, lines, and polygons, imagery, surface elevation, cell-based grids, or virtually any data feed that has location (for example, weather gauges, traffic conditions, security cameras, and tweets). Additional examples of layers include earthquake epicenters, historical traffic patterns, terrain, 3D buildings, and parcels. The type of layer indicates how you can interact with the layer’s data. For example, you can view and query the data in a feature layer to see a feature’s attributes. You may also be able to edit the data represented by the feature layer. With tile layers, you only see tiled images of the features.

Layer types include the following:

• Map image layer—A collection of map cartography based on vector data. Vector data includes points, lines, and polygons. Map image layers are dynamically rendered image tiles.
• Imagery layer—A collection of map cartography based on raster data. Raster data is a grid of cells commonly used to store imagery and other information captured by remote sensing devices. Imagery layers can be displayed dynamically or prerendered as cached image tiles.
• Tile layer—A set of web-accessible tiles that reside on a server. Tile layers can include prerendered map image tiles or vector tiles.
• Elevation layer—A collection of prerendered cached image tiles in the Limited Error Raster Compression format (LERC). LERC is a compression format for single-band or elevation data. Elevation layers are suitable to show terrain in scenes at global and landscape scale.
• Feature layer—A grouping of specific geographic features. Each feature in the collection has a location, set of properties, map symbology, and pop-ups. A feature layer allows you to execute queries on the point, line, and polygon features, perform live edits on the features using templates, and perform analysis on the features. The contents of some feature layers can be downloaded. Streaming features can be the source of feature layers.
• Scene layer—A collection of 3D feature objects and z-values (elevation value). A scene layer can be the following types: point, 3D object, integrated mesh, or point cloud.
• Table—A collection of rows and columns, where each row, or record, represents a feature—such as a parcel or power pole—and each column, or field, describes a particular attribute of the feature, such as its square footage, height, or length. Tables can include location information, such as addresses, or no location information, for example, a simple list of names and salaries.

Within an ArcGIS portal, web layers are categorized by the type of data they contain—for example, elevation, feature, or imagery. This helps make the connection about what is displayed in the map. Icons also help show the type of data in the layer. The source of web layers is described on the item page.

The data used in layers can be provided by a variety of sources, including ArcGIS Online hosted services, ArcGIS Server services, CSV files, KML files, feature collections, and OGC services. Layers are not only the data, however. A layer represents both data and the visualization applied to it. Visualization can include the symbology used to display the data, as well as pop-up configurations, filters, and other configurations.

Layers and data

The fundamental types of data that can be displayed in a map are features and imagery. Different types of layers have different capabilities. For example, publishing data in a CSV file creates a feature layer. Feature layers give you the ability to query and edit features in client applications, and manage access to the actual data.

Some layers—such as feature layers and imagery layers—provide access to the underlying data, while others—such as tile layers and scene layers—are visualizations of the data, optimized for a particular use. You can host your data in ArcGIS Online or reference layers that live in a GIS server. Publishing your data to ArcGIS Online allows you to host, or store, your data in ArcGIS Online by creating layers that represent this data. These layers are called hosted web layers. When you publish data as a hosted web layer, the layer contains the data. ArcGIS Online can host feature layers, tile layers, scene layers, and WFS layers.

You can also have layers that reference the data in a GIS server. For example, if you register your ArcGIS Server map service as an item, a layer that contains a reference to your map service is created. The data still resides within your map service and is not copied to ArcGIS Online.

You can also create alternate views of hosted layers. This is done by making copies of layers or creating hosted feature layer views, as described in the following sections.

Copies of layers

You can create a copy of a layer, which will copy the layer’s configuration to the new layer. Typically, the data associated with the layer is not copied; the layer maintains a reference to the data. If the data is updated, any layers referencing it will reflect the updated data. This is particularly advantageous when you have data with multiple attributes. Different layers may represent the same data but are displayed using different visualizations. Each layer could be styled based on different attributes. While the data is the same between each layer, the different styling empowers you to focus on a different story with each layer. A layer can be included in multiple web maps and web scenes, meaning configurations you’ve saved with the layer will be honored in any web map that includes the layer.

Hosted feature layer views

If you have publishing privileges and need a different view of your hosted feature layer beyond changing its style and presentation—for example, you want to apply different editing capabilities or share the data with different groups—you can create a hosted feature layer view from your hosted feature layer. A hosted feature layer view is similar to a copy of a layer but is more powerful because it allows you to control more than just how the layer is displayed. For example, you might create a hosted feature layer view when you need to support different editing capabilities for different groups of people. Many organizations need to share data with the public and simultaneously allow members within the organization to keep that data up to date. Hosted feature layer views provide a direct way to do this. When you publish your hosted feature layer, you can share it with particular members of your organization who need to edit it. Then, for the general public, you can create a hosted feature layer view that references the original hosted feature layer but with editing disabled. Because the two layers share the same data, as members edit the original hosted feature layer, the general public will see those changes immediately.

When you create a hosted feature layer view, a new feature layer item is added to My Content. Because it is a separate layer, you can change its style, filters, and sharing properties without affecting the source hosted feature layer. However, because the hosted feature layer view accesses the same data as the hosted feature layer it was created from, updates made to the data through the original hosted feature layer appear in the hosted feature layer view. Similarly, if you edit the data through the hosted feature layer view, your changes appear in the hosted feature layer. Only the owner of a hosted feature layer can create a hosted feature layer view from the original layer. This is different than copying a layer, which can be done by non-owners and even public users.

Maps, scenes, and layers

Web maps and web scenes are collections of layers and are the primary way to interact with layers through apps. Every map and scene contains a basemap and may also contain other layers that are drawn on top of the basemap. Basemap layers are typically used for viewing purposes or context only and are usually tile layers, map image layers, or imagery layers. The layers drawn on top of the basemap can be features or imagery and are called operational layers. Operational layers are the layers you interact with. Interactions include viewing attribution information, editing features, and performing analysis. While the visualization of the layers in a map or scene is configured on the layer, properties such as extent, visibility, and layer order are configured on the map, enabling you to control how the layer collection is displayed within the map or scene.

Maps, scenes, and layers can be managed as items in ArcGIS Online. These items are displayed to you in My Content and are shareable with others and searchable in ArcGIS Online. While many layers are available as items in ArcGIS Online, in some cases, layers are not available as items; the layer is only available within the web map containing it. For example, you can add a CSV file directly to a map. In this case, the feature layer created by adding the CSV file is only available in the map and not as a separate item.