Basic Analysis and Graphing - SAS

424 Creating Maps Chapter 16
Background Maps
If you look at the axes values, you can see that the area is less than 1/10° by 1/10°. The Simple Earth and
Detailed Earth background maps do not display that type of resolution. The NASA server provides a fairly
detailed view of any land mass on Earth. Water, however, is simply filled in as black. The NASA server is free
to access, but it is also limited in availability. If the server is temporarily unavailable or becomes overloaded
with requests, it delivers an error message instead of the requested map.
Another Internet-based option for background maps is a Web Map Service (WMS). The WMS option
enables you to specify any server that supports the WMS interface. The NASA server is an example of a
WMS server, but we have provided the URL and a layer name for you. With the WMS option, you must
know the URL to the WMS server and a layer name supported by the server. Most WMS servers support
multiple layers. For example, one layer can show terrain, another layer can show roads, and still another
layer can include water, such as rivers and lakes. By specifying the URL for the server and the layer, JMP can
make a request to the server and then display the map that is returned.
Unlike with simple and detailed maps, WMS maps do not wrap. You can scroll horizontally and vertically.
However, beyond the -180 to 180 (x axis) and -90 to 90 (y axis) ranges, a plain background appears instead
of the map. The limits of the axes are used to define the limits of the map that is displayed.
In order to use the WMS option for a background map, you need to decide which WMS server to use.
There are many WMS servers freely available from the Internet. Most of them provide maps only for a
particular area of the world, and each of them supports their own layers. So you have to search for the
appropriate WMS server for your particular situation.
You can search for WMS servers on the Internet using your favorite search engine. Once you find one, you
need to discover the layers that it supports. For this, you can use the WMS Explorer add-in. The WMS
Explorer add-in generates a list of all the layers available on a server. You can select a layer from the list to see
what it looks like. You can download the WMS Explorer add-in from the JMP File Exchange page.
Note: To use the WMS Explorer add-in and the WMS background map capabilities of JMP, your
computer must be connected to the Internet.
To locate a server, launch the add-in through the menu items Add-Ins > Map Images > WMS Explorer. 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 (the list can be out of date). After specifying
a WMS server, select Get Layers. Using Get Layers is not necessary if selecting from the drop-down list or
if clicking Enter after entering a URL. This sends a request to the WMS server for a list of layers that the
server supports. The returned list appears in the list box on the left, labeled Layers. A map of the world
appears as an outline in the graph to the right. Selecting a layer makes a request to the WMS server to return
a map, using the specified layer, that represents the entire earth. Selecting a different layer generates a
different map.
It is important to note that not all maps are generated to cover the entire earth (for example, some WMS
servers might provide mapping data for a particular county, within a state). In that case, it is likely that
selecting a layer will not generate any visible map. You might have to zoom in on the appropriate area before
any image map is visible. The standard JMP toolbar is available in the add-in window and the zoom tool
works just like it does in any JMP window.