Web Mapping Service, Web Coverage Service, or Web Feature Service – What’s the Difference?
If you have ever attempted to establish a remote connection to data, you have likely come across the terms: Web Mapping Service (WMS), Web Coverage Service (WCS), and Web Feature Service (WFS). From time to time, I find myself having to revisit these terms so I thought I’d use this blog post to go over the subtle,but important, differences between these services.
First of all, it’s probably important to note that the specifications for these services have been defined by the Open Geospatial Consortium (OGC). The OGC is an international industry consortium of over 480 companies, government agencies, and universities that participate in a consensus process to develop publicly available interface standards. Adhering to OGC standards for the exchange of geospatial data means that products or online services can essentially interoperate, or "plug-and-play", even though they are developed independent of one another.
Web Mapping Service (WMS) – A standard protocol for serving georeferenced map images over the internet that are generated from a map server using data from a GIS database. It’s important to note that with a WMS, you are essentially getting an image of geospatial data (i.e. JPG, GIF, PNG file). While this has its uses, it is an image only, and therefore does not contain any of the underlying geospatial data that was used to create the image.
Web Coverage Service (WCS) – A standard protocol for serving coverage data which returns data with its original semantics (instead of just pictures) which may be interpreted, extrapolated,etc., and not just portrayed. Essentially,a WCS can be thought of as the raw geospatial raster data behind an image. Using a WCS, you can pull the raw raster information you need to perform further analysis.
Web Feature Service (WFS) – A standard protocol for serving geographical features across the web using platform-independent calls. A WFS can be thought of as the vector geospatial data behind a map. Using a WFS, you can pull only the vector file information that you need and apply it to a wide variety of purposes, including purposes other than the producers’ intended ones.
So, to give a quick summarization, a WMS is simply an image of a map. You can almost think of this like taking a screenshot of Google Maps. A WCS is the raw raster data, so for example, if you are working with a WCS containing Landsat imagery, you can effectively chunk off the piece you are interested in and download the full multispectral image at the spatial resolution of the original image. A WFS contains the vector data behind a map. The beauty of these services is that you can grab only the information you need. So, rather than retrieving a file that contains the data you are seeking and possibly much more, you can confine your download to only your area of interest, allowing you to get what you need and no more.