Spot the Difference: Comparing Web Services
ArcGIS Online and ArcGIS Enterprise let you access your GIS resources as web services. But those web services come in many variations. It’s not always easy to tell what you are working with.
Map Image Layer vs Feature layer
Fig. 1: Map Image Layer
Fig. 2: Feature layer
These two images show two different layer items published together from the same data. The top image shows a Map Image Layer. When you load a Map Image Layer into a map, the server sends an image of what will be displayed in the map.
The bottom image shows a Feature layer. When you load a Feature layer into a map, the server sends the coordinates of the vertices for every feature, and your client uses that information to draw the image on your end.
Map Image Layers have the advantage of supporting more advanced symbology, because the server renders the image. Feature layers have the advantage of supporting editing, because you get the actual coordinates of the geometry (but there are some nuances that we will get into later).
Feature layers are available in both ArcGIS Online and ArcGIS Enterprise. Map Image Layers are available only in ArcGIS Enterprise.
Feature layer vs. hosted feature layer
Fig. 3: Feature layer
Fig. 4: Feature layer
The top image shows the same Feature layer from the previous pair. The bottom image is a different kind of Feature layer, called a hosted feature layer. Both types of Feature layer support editing, but the underlying technology that enables each type is different.
The data for a hosted feature layer must be copied into ArcGIS. The data for a non-hosted feature layer can be in a user-managed data store, like an enterprise geodatabase. The advantage of hosted feature layers is that they use less server memory than a non-hosted feature layer. One advantage of a non-hosted feature layer is that you can use advanced database features like versioning and topology. You also have more control over configuring non-hosted feature layers, but that control comes with more responsibility for configuring them correctly.
Hosted feature layers are available in both ArcGIS Online and ArcGIS Enterprise. Non-hosted feature layers are available only in ArcGIS Enterprise.
Feature layer vs. feature service
Fig. 5: Hosted feature layer with URL
Fig. 6: Feature service with Service Item Id
These images look so radically different that the real challenge might be finding ways they are similar. The top image is for the same hosted feature layer item in the previous pair. The bottom image is for the feature service for that hosted feature layer item. You can tell the two are related because the Service Item Id in the bottom image matches the id value in the URL in the top image.
A service defines a set of capabilities. You may have heard people talk about a “REST endpoint”, which refers to the service’s URL used to access those capabilities. You can see some of the service’s capabilities in the bottom image: it is not versioned, it can be queried, it returns a maximum of 2000 records for a single query.
A layer item is a particular configuration on top of a service’s capabilities. Symbology is one layer configuration. Pop-ups, labeling, and filtering are other layer configuration properties.
The relationship between services and layer items has two important implications. The first is that you can have multiple different layer items that all reference the same service. The second is that different types of layers have different types of services as their source: feature services for Feature layers (whether hosted or not) and map services for Map Image Layers.
This model of related services and layers applies to content in both ArcGIS Online and ArcGIS Enterprise.
To get the most out of your web resources, it is important to know the differences among Map Image Layers, hosted Feature layers, non-hosted Feature layers, feature services, and map services. Understanding the purpose, advantages, and limitations of each will enable you to make the right choice for your use case.
Related Resources
For further ArcGIS Online training, check out Esri's ArcGIS Online: Essential Workflows course: https://bit.ly/36FfoOQ. For further ArcGIS Enterprise training, checkout Esri's ArcGIS Enterprise: Administration Workflows course: https://bit.ly/37AZVzI.