WMS: Web Map Service

WMS最早是由OGC提出的，现在已经被ISO所采纳，形成了ISO 19128标准。
WMS提供了3个操作来支持创建和显示地图。
WMS分为客户端和服务器端。客户端支持意味着可以使用别的WMS服务器端。

The OpenGIS® Web Map Service (WMS) Implementation Specification provides three operations (GetCapabilities, GetMap, and GetFeatureInfo) in support of the creation and display of registered and superimposed map-like views of information that come simultaneously from multiple remote and heterogeneous sources.

When client and server software implements WMS, any client can access maps from any server. Any client can combine maps (overlay them like clear acetate sheets) from one or more servers. Any client can query information from a map provided by any server. While programmers need to write code to implement the specifications, end users can take advantage of products that include them to publish and access geospatial information. Software buyers can choose the best solution for their needs and not worry about if it will work with other solutions; if they all implement the same standard, WMS, they will all work together.

In particular WMS defines:

1. How to request and provide a map as a picture or set of features (GetMap)
2. How to get and provide information about the content of a map such as the value of a feature at a location (GetFeatureInfo)
3. How to get and provide information about what types of maps a server can deliver (GetCapabilities)