In this book you're going to use the ArcGIS API for JavaScript Sandbox to write and test your code. The Sandbox can be found at https://developers.arcgis.com/javascript/3/sandbox/sandbox.html and will appear as seen in the screenshot when loaded. You'll write your code in the left pane and click the REFRESH button to see the results in the right pane:

Now that we've got some of the basics of HTML, CSS, and JavaScript out of the way it's time to actually get to work and learn how to build some great GIS web applications! The material in this chapter will introduce you to some of the fundamental concepts that define how you create a map and add information to the map in the form of layers.

There are several steps that you'll need to follow for creating any GIS web application with the ArcGIS API for JavaScript. These steps will always need to be performed if you intend to have a map as part of your application. And I can't imagine that you wouldn't want to do that, given that you're reading this book! In a nutshell,there are several steps you need to follow:

• Create the HTML code for the page
• Reference the ArcGIS API for JavaScript...

You'll need to follow the preceding process we described for every application that you build with the ArcGIS API for JavaScript.

The creation of the map can only happen when your HTML has finished loading, and all the required DOM elements and scripts are ready. You achieved this by using the domReady! plugin in your require() function. This ensured that the code in the function that was passed as the second argument only executes when everything is in place. This function is known as an initialization function:

require(["esri/map", "dojo/domReady!"], function(Map) {
  // initialization goes here
});

You use your initialization function to create your map, add layers, and perform any other setup routines necessary to start your application.

Creating a map is invariably one of the first things that you'll do and in this section we...

A map without data layers is like an artist with a blank canvas. The data layers that you add to your map give it meaning and set the stage for analysis. These data layers come from map services published by ArcGIS Server and, occasionally, other GIS servers. The two main types of layers available from ArcGIS Server are dynamic map service layers and tiled (or cached) map service layers.

Dynamic map service layers reference map services that create a map image on the fly and then return the image to the application. This type of map service may be composed of one or more layers of information. For example, the Demographics map service displayed in the following screenshot is composed of nine different layers representing demographic information at various levels of geography:

While they can take somewhat longer to display in a client application...

In programming, events are actions that take place within an application. Normally these events are triggered by the end user and can include things like mouse clicks, mouse drags, keyboard actions, and others, but can also include the sending and receiving of data, changes in state of a user interface component, and many other scenarios.

The ArcGIS API for JavaScript is an asynchronous API that follows a publish/subscribe pattern wherein an application registers (publishes) events with listeners (subscribers). The following diagram illustrates this process. Listeners are responsible for monitoring the application for these events and then triggering a handler function that responds to the event. Multiple events can be registered to the same listener. The dojo on() function creates a listener that associates an event to a handler function:

As you'll recall the...

We covered a lot of ground in this chapter. All applications created with the ArcGIS API for JavaScript require you to perform certain steps. These include defining references to the API and style sheet, loading modules, creating an initialization function, and so on. In the initialization function you will most likely create an instance of the Map class, add various layers, and perform other setup operations that need to be performed before the application is used. In this chapter you learned how to perform these tasks.

In addition, we examined the various types of layers that can be added to a map including tiled map service layers and dynamic map service layers. Tiled map service layers are pre-created and cached on the server and are most often used as basemaps in an application. Dynamic map service layers must be created on the fly each time a request is made and...