What is an API?
An API, or Application Programming Interface, is how an application can access a server. It provides a way to send and receive information and functionality between your application and a server in an easy-to-use format, usually JSON.
For example, say you built an application that got a all the tags for all of a user’s items in ArcGIS Online, and sorted those tags by most popular. You could sign into ArcGIS Online, view that user’s content, and manually make a list of all the items and their tags. However, this would be limited to what that user had shared with you, and your list would become out of date as soon as they edited any tags, added a new item, or deleted an old one.
Your data is important. As such, you want to make sure you can control who can access and edit that data. Therefore, authentication is an obvious first choice when looking at the benefits of working with this API. Using the OAuth and IdentityManager classes, information on the signed in user is included with almost every request automatically. This means there is almost no work needed in order to ensure that users can only access item and information they’re supposed. You can also control these settings using the 3.x version of the API. For more information, see our guide on OAuth 2.0 and ArcGIS.
While the example above just shows a 2D and 3D map displayed at the same time, the ability to use both together can be used in a variety of ways. For example, you could allow a user to navigate to a certain location on a globe using a 3D map, and update a 2D map to display the same location, or vice versa. This can allow users of an application to see data that may have been recorded only in 2D or 3D format along with data that is stored in another format. You could also create a 3D mapping application, but allow users to toggle to a 2D application if their network, browser, or device cannot handle processing a 3D mapping application. This would mean you can make a more versatile application rather than having to repeat your work and maintain two different versions of the same application.
The Dictionary Renderer will allow you to symbolize the features on your map using multiple attributes together. You can define and combine symbols, giving you an impressive degree of flexibility and control when displaying your data. Check out a cool example of how the class can be used to display different features at California gas stations to get some ideas on how you might use it.