Web maps often contain a basemap, which provides a geographic frame of reference, and operational (or thematic) layers, which show a focused item of interest on top of the basemap. A familiar example might be an online mapping service that provides real-time traffic information on top of a city street map. The street map is the basemap. It doesn't change much and can be used for many purposes. The traffic information is the operational layer because it frequently changes and has a specific purpose and audience. This topic describes different patterns for building web applications that overlay basemap and operational layers.
Basemaps and operational layers often require separate strategies for effective maintenance and display in web maps. When creating a web map, it's a good practice to separate the basemap from the operational layers. Basemaps generally require little maintenance and should almost always be cached, whereas operational layers may require creative strategies to present the most current data in a high-performance way.
Separating your basemap and operational layers requires that you create at least two map documents, which you subsequently use to publish two distinct map services. Each becomes a map service layer in the overall web map. A map service layer originates from a map document that may itself contain many layers.
This may seem strange to you if you're new to web mapping; perhaps your company has one map document with dozens of layers that it's used for years. For performance and flexibility reasons, it may be time to break up that monolithic map document. When you create multiple map documents, each containing a logical group of layers—basemap features, cadastral features, and so on—you can publish them as separate services and target your display strategies for each.
The way that you'll be using the services affects how you design the map. For example, if you're creating a basemap that your business data will overlay, it's good practice to use neutral colors that won't dominate the map. Another important consideration is that transparencies of individual layers in a map service do not always persist in the image that the server exports. Transparency should normally be applied at the client tier to the map service as a whole.Feedback on this topic?