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JohnPonte

Staff

Joined:

Jun 17, 2013

WMS Explorer Add-In

The WMS Explorer Add-in is designed to help a user locate and explore the Web Mapping Service (WMS) provided by a WMS server. A WMS server provides a map, as an image, based on GIS data stored by the server. 

Beginning with JMP 9.0, a background map can be added to a graph by bringing up the background map dialog. The dialog allows you to specify a source for an image (raster) map as well as a boundary (vector) map. A WMS server can be used as the source for an image background map. To specify a WMS server as a background source, simply specify the url of the server as well as a layer (or layers) that the server supports. Layers are unique to each server so you must know what layer name(s) are provided by the WMS server. The WMS Explorer Add-in can help determine appropriate server urls and layer names.

The Add-in presents a text box for entering the url of a known WMS server. Alternatively, you can make a selection from a drop-down list of pre-discovered WMS servers. After specifying a WMS server,  select the "Get Layers" button. (Using the "Get Layers" button is not necessary if selecting from the drop-down list or if hitting the enter key after typing in a url). This will send a request to the WMS server for a list of layers that the server supports. The returned list will appear in the list box on the left, labeled "Layers". A map of the world will appear as an outline in the graph to the right. Selecting a layer will make a request to the WMS server to return a map, using the specified layer, that will represent the entire earth. Selecting a different layer will generate a different map. You may also select multiple layers by using the shift and control keys while selecting.

It is important to note that not all maps are generated to cover the entire earth. Some WMS servers provide mapping data for a particular country, state or even a county. In that case, it is likely that selecting a layer will not generate any visible map. You may have to zoom in on the appropriate area before any image map is visible. The standard JMP tool bar is available in the Add-in window and the zoom tool works just like it does in any JMP window.

Once a desirable map is determined, simply note the url in the text box at the top and the selected layer in the "Layers" list. This is the information that will be input into the background map dialog when WMS is selected as the type of image background map. You can enter more than one layer in the dialog by creating a comma separated list of layer names.

Because requests are being made to a server across the internet, there are a number of conditions that can generate an error. WMS servers often have limited availability and sometimes are not available at all.  Occasionally a WMS server may return a name of a layer that it no longer supports. In these types of cases (and others), a server will usually return an error message in lieu of a map. If that happens, the error message will be displayed below the "Layers" list in an area labeled "Errors".

There are MANY more WMS servers than the ones provided in the drop-down list. Doing an internet search can deliver loads of possibilities. The "best" WMS server to use will be unique for each user and each situation. Here are a few links to help you begin your search.

http://www.skylab-mobilesystems.com/en/wms_serverlist.html
http://geoserver.org/display/GEOS/Available+WMS+and+WFS+servers
http://www.mapmatters.org/

You can find more information about using background maps in JMP by reading some of my blog posts on the JMP blog site at http://blogs.sas.com/content/jmp/author/johnponte/

Enjoy!