When working with cartography, often you cannot have all the information you need stored in your device, instead you can remotely access and visualize using a WMS service (Web Map Service) which is a protocol for serving georeferenced map images (jpeg, png, tif) which a map server generates using data from a database (Wikipedia) in simple words, you can ‘see’ georeferenced information (maps) in your computer and use it to create cartography, using it a basemaps.
In this brief exercise I will show you how to add a WMS to QGIS, information that can be used to prepare cartography. For easiness I will use a WMS I previously used, but the general dynamic is the same.
The WMS service, the OpenGIS® Web Map Service Interface Standard (WMS) provides a simple HTTP interface for requesting geo-registered map images from one or more distributed geospatial databases. A WMS request defines the geographic layer(s) and area of interest to be processed. The response to the request is one or more geo-registered map images (returned as JPEG, PNG, etc) that can be displayed in a browser application (Opengeospatial consortium). In this case we will use the QGIS capabilities to access and display information using a WMS server. A distinction should be done, a WMS is not a web site even though it looks like a website it gives the parameters to establish the connection between the application and the map server.
Getting a WMS server, for this case I will use the WMS services provided by the Military Geographic Institute from Ecuador which allow to access to different kind of information at different scale and resolution. In this case I chose the WMS for orthophotography for Ecuador. Once you click on a WMS service link you will get something similar to this:
Well as a website or as a text file with the WMS service URL as in this case. Remember it is not a website if you copy it and paste in a web browser you will see nothing but weird numbers and letters.
Keep the address, we will need it in the next steps.
It will display a window were we will add the WMS service to our map.
In this window all the services we add will be listed and can be used in future sessions, as it is our first time using this option it is normal that this list is empty.
If we click in New the connection details window will pop up:
In the name field we will add a name to our connection, in this case I will use the name ‘Orto_IGM’ and in the URL field we will paste exactly the same url we got in the previous step. The fields: user name and Password sometimes are required when accessing restricted services, but in this case we leave them blank since this service is free.
If we click in Ok, the window will close and the new service will be shown in the list.
Select it and click in Connect, this action will establish the connection between your application and the WMS server. In the lower part all the available layers within the service will be shown and we can choose which of them we want to add to our map.
For this example I chose the igm:volcan_cotopaxi_2011 layer which contains a orthophoto of the Cotopaxi volcano from the year 2011, which normally is not accessible for downloads. Once the desired layer is selected, click in Add and the layer will be displayed in the map view.
And that’s it! Now you know how to add layers from a WMS server to QGIS and how to use it to create maps. You can also add your own layers like in this case, I added the height contours over the orthophoto (in blue) and both layers can be used to create maps, but this is material for other day.
Recommendations and tips
- To use WMS servers you need internet (Yes I know it is quite limiting).
- Normally you cannot download the information you see through the service to your local drive, yet, you can use it to create maps which can be printed.
- In my personal experience this services (depending on the kind of displayed feature) will require high amounts of data and depending on your internet connection speed it might be slow.
- These services provide with interesting sources of information but also possess some limitations which can be overcome with other services like the WFS.
Written by: Marlon Calispa