Using ArcGIS Velocity, you can write output observations and analysis results to feature layers or stream layers for visualization in web maps.
Feature layers
A feature layer is a grouping of similar geographic features, for example, buildings, parcels, cities, or roads. With Velocity, you can store Internet of Things (IoT) observations from sensors as features to explore visually on a map such as current vehicle locations, temperature readings, or earthquake epicenters. IoT observations represented as features can be points, lines, or polygons (areas). For more information about the types of feature layers in ArcGIS, see Feature layers.
Since feature layers represent data as points, lines, and polygons, they can be used to visualize data in a variety of ways. For example, temperature readings can be displayed in a common blue-yellow-orange-red sequence of colors to indicate areas that are cooler or warmer. Conversely, the same temperature data can be displayed relative to a threshold that is important to specific workflows such as everything below 50 degrees Fahrenheit representing temperatures of concern and temperatures above being acceptable.
Feature layer rendering can be defined in a web map. In Velocity, to visualize collected IoT observations or analytic results, click the map button next to the layer on the Layers page. This opens the layer in a new web map and provides many styling options. For more information about styling feature layers, see Change style.
When to use feature layers
Feature layers can be used to visualize observation data, with a wide variety of styling options and query capabilities available. Use feature layers to explore lower volumes of observation data over time or when sensor data is not changing rapidly. When storing data in feature layers with Velocity, every feature layer has an associated map image layer that you can use to visualize high volume data as dynamic aggregations to see broader patterns more easily. For more information, see Visualize map image layers.
Stream layers
A stream layer is a feature layer that is optimized for the visualization of real-time data. Feature layers display information that has been stored, and new information is visualized by regularly refreshing the feature layer in a web map. Stream layers display observations in the web map as soon as they are received by the server. This is effective for sensor data that changes rapidly or irregularly or for tracking workflows in which assets or field crews need to be continuously monitored. In Velocity, feeds behave similar to a stream layer when added to a web map.
To receive real-time data immediately, a stream layer connects to an underlying stream service using HTML5 WebSockets. The stream layer is then a client to the WebSocket, and incoming data is broadcast to all connected clients as soon as it is received. Most modern web browsers support WebSockets.
When working with stream layers in Velocity, you can control stream feature layers to filter the data that the service sends to the layer such as limiting the incoming data to observations in the current map extent. Because stream layers are a type of feature layer, many of the same rendering styles are available. For more information about setting advanced renderers, see the Stream Layer and StreamLayerView documentation in the ArcGIS API for JavaScript help.
When to use stream layers
Stream layers can be used to display fast-moving observations on a map or when you do not want to regularly query your data store to display new information. Stream layers are also ephemeral, meaning the incoming data is not persisted separately from the client session. This can be useful when information is used largely as a visual aid such as monitoring weather patterns during a large sporting event. For details, see Visualize stream layers.