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Building operational map layers |
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Release 9.3
Last modified August 13, 2008 |
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Each map application requires a set of operational map layers for use by a particular group of users. For example, users can display observations, sensor feeds, and query results on top of their base map to perform a series of work tasks and to address specific missions and goals. These information overlays provide a set of "operational layers." Each operational layer will probably also include a set of tools that are used to work with the map layer.
Some of the most common the types of operational map layers are described here, which will help you with ideas about the types of operational information that you want to serve.
Characteristics of operational map layers
- Operational map layers are the ones that your end users will view and work with to perform their daily work.
- They are typically delivered as additional, independent map services that you draw on top of your base map service in your GIS map application.
- There can be more than one operational layer in any GIS map application. However, you will typically want to limit the number of operational layers that your users work with to just a few, focused map layers.
- Operational map layers should be responsive. They should draw quickly and efficiently. Their contents should be up-to-date and reflect the current status that is relevant for the kinds of decisions that these map layers will support. They should be easy-to-use and understand. These aspects of operational map layers will influence how you design their display properties in the ArcMap documents and also how you will publish operational map layers for your users.
- If you are responsible for publishing GIS services, you will typically publish each operational map layer as a separate Web map service.
- Each independent operational map layer will be created as a stand-alone ArcMap document.
- In most applications, the operational map layer must be in the same coordinate system as your base map service. This is relevant for simple client applications that cannot perform map projection on the fly (e.g., in Web browser applications, ArcGIS Explorer, Google Earth, and so forth).
- You will need to define the set of tools and functions that your users will apply to work with the information in each operational map layer. See Tasks and tools in the GIS application for more information.
NOTE: It is also worth noting that some of the datasets that are used in your GIS base map will also frequently be used as data sources for operational layers in your web map applications. When you plan your design for this, you will want to consider how your operational map layers for these datasets will overlay onto and work well with your base map.
Three methods for publishing operational map services
There are three common methods used to publish operational map services for end users to employ in their GIS map applications:
- As a dynamic map service using ArcGIS Server
- As a cached map service using ArcGIS Server
- Using queries to select a subset of features that meet particular criteria, and then displaying the query results using map graphics and text.
1. Publishing dynamic map services
One of the types of map services that you can publish using ArcGIS Server is a dynamic map service. As the name implies, the map layer display is dynamically generated. In other words, the display is computed and served each time you make a request to the server to display the map service. The resulting map image is sent to the requesting application and overlaid on the base map.
To create a dynamic map service that is served using ArcGIS Server, you first need to create an ArcMap document (.mxd) in ArcMap and then publish it as a map service. The resulting map service will be consumed in Web GIS map applications as a single map layer.
The ArcMap document for an operational layer should be very simple and contain only a single or a few focused map layers. The resulting map service provides access to the data, allowing you to display and work with the operational information.
This dynamic map service is usually displayed on top of a base map service. Operational map layers are often combined with a small number of other focused operational map layers that are displayed together to provide a status map.
You can create a map document in ArcMap that references a map layer that will undergo frequent updates or be produced as the results of an analytical model. For example, if you have users who will edit a map layer in the Web map application, this map layer would certainly have to be dynamic. In these and many other cases, you want to compute the map layer each time that you go to draw the map.
Dynamic map services have the advantage of providing an up-to-date and accurate status for the operational layer. However, dynamic map layers can often be slow to compute and display. Therefore, it is important to design dynamic map layers that use efficient map symbols and labels and whose map views can be computed quickly.
Here is a checklist of things to consider for dynamic map services.
| Checklist item | Links to further information |
| Use simple map symbols that draw efficiently, such as the ESRI_Optimized style. | See Displaying layers in interactive maps.
Also, see Optimizing map symbology for performance. |
| When you can, create a map document for your dynamic map service that is in the same coordinate system as your base map.
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See Specifying a coordinate system for your map. |
| Follow the guide for publishing map services with ArcGIS Server
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See Tips for preparing map documents that will be published as services |
2. Publishing cached map services
Another alternative for serving operational map layers is to use a cached map service where the map display is pre-computed and stored in a map cache ahead of time. In these cases, there is no need to recompute the display of the operational map layer each time that a user requests a map from a server. Instead the appropriate map tiles are retrieved from the server, which greatly increases performance and scalability in most cases.
In some cases, operational map layers are more static and change less frequently. This means that you can update them periodically by pre-computing the map as opposed to computing a new map every time one is requested from the server. This way, everyone can access a faster, more efficient map service that they will work with.
One slight variation of using a cached map service is to use on-demand caching. When the first user hits the map server, the map cache is computed for the requested area (for a set of map tiles), and the cache is built. Anyone else who visits the same map tiles, simply uses the new map cache. Each time a user makes a request, it retrieves that cached map tile if it exists. Otherwise, it computes the tile and caches it. Only the first user needs to compute the map display, and then other users can hit a cached map of the operational layer.
On demand map caches are often easier to maintain than those where the entire map layer must be pre-computed.
This enables you to leverage cached map services in order to get the highest level of performance and scalability in your maps. Many times, you can automate the caching of operational map layers so that they can be computed once and used by many users (or by the same user who may re-visit an area time and again during the same map session).
See Tips and best practices for map caches for more information on building cached map services.
3. Displaying query results as map graphics and text
One of the most efficient mechanisms for displaying operational information is to use the results of a query. You query the GIS server, which returns a set of feature results as a small record set. Query results that are returned from the server include a set of features, their coordinates, and a set of each feature's attributes. These results are displayed on the map as interactive graphics and descriptive information that can be worked with, charted, summarized and used as hyperlinks that can be clicked to access more detailed information about each feature.
This approach requires application programming to create the map layer of results. Refer to the following links for more information:
See these examples for how to use query results in JavaScript applications
See these examples for using query results in the Web Mapping Application using .NET
See these examples for using query results in the Web Mapping Application using Java
How to combine cached maps with dynamic map services
Each Web GIS map application that you build will consume a small set of map services. At least one of the map services will provide the base map for your application. Other services can be added for each operational layer that you want to use in your application.
Often there is a one-to-one correspondence between each map layer in your Web GIS map application and the number of GIS services being accessed.
This web map contains two primary map services - the shaded relief map service which acts as the base map and a series of map layers for California.
When you assemble your GIS map application, you will identify the set of map services to be accessed and their Web connections (a list of URL's). In many map applications, you will need for each map service to use the same coordinate system.