An ArcGISDynamicMapServiceLayer is the default type of map published through the ArcGIS Server. It is a dynamic map, meaning that its content is updated whenever the map is refreshed. Because it is dynamic, the data can also be reprojected to fit on another map layer that is not in the same spatial reference.

require(["esri/map", "esri/layers/ArcGISDynamicMapServiceLayer"], 
  function (Map, ArcGISDynamicMapServiceLayer) {
  …
  var map = new Map("mapdiv", {…});
  var layer = new ArcGISDynamicMapServiceLayer ("http://serv.er/arcgis/rest/services/MyDynamicLayer/mapserver");
  map.addLayer(layer);
});

Because the data within an ArcGISDynamicMapServiceLayer is dynamic, ArcGIS Server redraws what the layer should look like every time the map looks at the data from a different location and zoom level. If this layer contains lots of labels, annotation, complicated graphics, or raster data (like aerial imagery, for instance), ArcGIS Server will require more system resources to render the map layer. This will lead to noticeably slower performance. Other services, like tiled map services, are recommended for that kind of data.

ArcGIS Server allows map services to be tiled. An ArcGISTiledMapServiceLayer has its content already drawn into images at scales defined when the map service is published. These images are stored on a hard drive for quick retrieval. The benefit is that these pre-rendered tiles are served quickly and with little effort on the part of the server. More map services can be run from the same machine with little effect on performance. See an example in the following code snippet:

require(["esri/map", "esri/layers/ArcGISTiledMapServiceLayer"], 
  function (Map, ArcGISTiledMapServiceLayer) {
  …
  var map = new Map("mapdiv", {…});
  var layer = new ArcGISTiledMapServiceLayer ("http://serv.er/arcgis/rest/services/MyTiledLayer/mapserver");
  map.addLayer(layer);
});

Tiled map services have some disadvantages. First, the data displayed through tiled map services doesn't change until the tiles are rebuilt. If a park boundary changes in the data, but the tiles aren't rebuilt, the service will still show the old boundary. Second, tiled map services restrict the map to specific zoom scales, with no easy way to view the map in between zoom scales. Third, if another tiled map is stacked on top of the first one, it not only has to be in the same spatial reference, but also the zoom scales have to overlap exactly within overlapping scale ranges. That means that a map built with scales of 1:500 and 1:1000 can be loaded with a map built with scales of 1:1000 and 1:2000, but a tiled layer with scales 1:750, 1:1500, and 1:3000 will not be seen.

We've seen ArcGIS layers that provide image data. Let's turn our attention to layers that handle more vector data.

GraphicsLayers provide a simple way to add custom vector graphics to your map. You can manage the graphics by calling add() and remove() methods on those graphics. You can also search through the list of graphics on the map by searching through the GraphicsLayer.graphics array.

As a side note, the map object has a built-in GraphicsLayer. You can access that GraphicsLayer through the map.graphics property.

FeatureLayers are specialized layers built on a GraphicsLayer that provide much more functionality. They have the custom vector graphics of a GraphicsLayer, plus they have an ArcGIS Server data source to populate the data. You can query for data by either location or attributes, add it to the map using custom graphics, and control popup content and styling. You can even edit data on your server.

Unlike ArcGIS Tiled and dynamic layers, which can mash up multiple layers at once, each FeatureLayer can only work with one map service layer. FeatureLayers can work with individual layers in a map service, or special editable map services called Feature Services. Feature Services provide more details about the map layer, including endpoints for querying results. If ArcGIS Server is configured to allow editing on the features, and the map service is published to allow editing, FeatureLayers that consume these services will let you modify both shape and tabular data.

Because FeatureLayers query data from ArcGIS Server, they are limited in the number of features they can return. Typically, ArcGIS Server limits the number of results returned in a query to one or two thousand, depending on the version. Server settings can be altered to show more results, but more FeatureLayer graphics on the map mean more memory is consumed, and the app may be slow and unresponsive. Careful thought must be put into using the FeatureLayer with your data.

One way that the FeatureLayer refines the number of features returned is by setting its mode. The FeatureLayer has three primary modes of feature selection:

We will look into FeatureLayers more closely in Chapter 5, Editing Map Data when we discuss editing.