.. _`wms-services`: |LS| Web Mapping Services =============================================================================== A Web Mapping Service (WMS) is a service hosted on a remote server. Similar to a website, you can access it as long as you have a connection to the server. Using QGIS, you can load a WMS directly into your existing map. From the lesson on plugins, you will remember that it's possible to load a new raster image from Google, for example. However, this is a once-off transaction: once you have downloaded the image, it doesn't change. A WMS is different in that it's a live service that will automatically refresh its view if you pan or zoom on the map. **The goal for this lesson:** To use a WMS and understand its limitations. |basic| |FA| Loading a WMS Layer ------------------------------------------------------------------------------- For this exercise, you can either use the basic map you made at the start of the course, or just start a new map and load some existing layers into it. For this example, we used a new map and loaded the original :guilabel:`places`, :guilabel:`landuse` and :guilabel:`protected_areas` layers and adjusted the symbology: .. figure:: img/new_map.png :align: center :width: 100% #. Load these layers into a new map, or use your original map with only these layers visible. #. Before starting to add the WMS layer, deactivate "on the fly" projection (:menuselection:`Project --> Properties... --> CRS` tab, check :guilabel:`No CRS (or unknown/non-Earth projection)`. This may cause the layers to no longer overlap properly, but don't worry: we'll fix that later. #. To add WMS layers, click on the |dataSourceManager| button to open the :guilabel:`Data Source Manager` dialog and enable the |addWmsLayer| :guilabel:`WMS/WMTS` tab. .. figure:: img/datasourcemanager_wms.png :align: center Remember how you connected to a SpatiaLite or GeoPackage database at the beginning of the course. The :guilabel:`landuse`, :guilabel:`buildings`, and :guilabel:`roads` layers are stored in a database. To use those layers, you first needed to connect to the database. Using a WMS is similar, with the exception that the layers are on a remote server. #. To create a new connection to a WMS, click on the :guilabel:`New` button. You'll need a WMS address to continue. There are several free WMS servers available on the Internet. One of these is `terrestris `_, which makes use of the `OpenStreetMap `_ dataset. #. To make use of this WMS, set it up in your current dialog, like this: .. figure:: img/new_wms_connection.png :align: center * The value of the :guilabel:`Name` field should be ``terrestris``. * The value of the :guilabel:`URL` field should be ``https://ows.terrestris.de/osm/service``. #. Click :guilabel:`OK`. You should see the new WMS server listed: .. figure:: img/new_connection_listed.png :align: center #. Click :guilabel:`Connect`. In the list below, you should now see these new entries loaded: .. figure:: img/new_wms_entries.png :align: center These are all the layers hosted by this WMS server. #. Click once on the :guilabel:`OSM-WMS` layer. This will display its :guilabel:`Coordinate Reference System`: .. figure:: img/osm_wms_selected.png :align: center Since we're not using ``WGS 84`` for our map, let's see all the CRSs we have to choose from. #. Click the :guilabel:`Change...` button. You will see a standard :guilabel:`Coordinate Reference System Selector` dialog. #. We want a *projected* CRS, so let's choose :guilabel:`WGS 84 / Pseudo Mercator`. #. Enter the value ``pseudo`` in the :guilabel:`Filter` field: #. Choose :guilabel:`WGS 84 / Pseudo Mercator` (with epsg:3857) from the list. .. figure:: img/pseudo_mercator_selected.png :align: center #. Click :guilabel:`OK`. The Coordinate Reference System associated with the entry has changed. #. Click :guilabel:`Add` and the new layer will appear in your map as :guilabel:`OpenStreetMap WMS - by terrestris`. #. Close the :guilabel:`Data Source Manager` dialog if not done automatically #. In the :guilabel:`Layers` panel, click and drag it to the bottom of the list. #. Zoom out in order to get a global view of the layers. You will notice that your layers aren't located correctly (near west of Africa). This is because "on the fly" projection is disabled. .. figure:: img/reprojection_off.png :align: center :width: 100% #. Let's enable the reprojection again, but using the same projection as the :guilabel:`OpenStreetMap WMS` layer, which is :guilabel:`WGS 84 / Pseudo Mercator`. #. Open the :menuselection:`Project --> Properties... --> CRS` tab #. Uncheck :guilabel:`No CRS (or unknown/non-Earth projection)` #. Choose :guilabel:`WGS 84 / Pseudo Mercator` from the list. .. figure:: img/enable_projection.png :align: center #. Click :guilabel:`OK`. #. Now right-click on one of your own layers in the :guilabel:`Layers` panel and click :guilabel:`Zoom to layer(s)`. You should see the |majorUrbanName| area: .. figure:: img/wms_result.png :align: center :width: 100% Note how the WMS layer's streets and our own streets overlap. That's a good sign! The nature and limitations of WMS ............................................................................... By now you may have noticed that this WMS layer actually has many features in it. It has streets, rivers, nature reserves, and so on. What's more, even though it looks like it's made up of vectors, it seems to be a raster, but you can't change its symbology. Why is that? This is how a WMS works: it's a map, similar to a normal map on paper, that you receive as an image. What usually happens is that you have vector layers, which QGIS renders as a map. But using a WMS, those vector layers are on the WMS server, which renders it as a map and sends that map to you as an image. QGIS can display this image, but can't change its symbology, because all that is handled on the server. This has several advantages, because you don't need to worry about the symbology. It's already worked out, and should be nice to look at on any competently designed WMS. On the other hand, you can't change the symbology if you don't like it, and if things change on the WMS server, then they'll change on your map as well. This is why you sometimes want to use a Web Feature Service (WFS) instead, which gives you vector layers separately, and not as part of a WMS-style map. This will be covered in the next lesson, however. First, let's add another WMS layer from the :guilabel:`terrestris` WMS server. |basic| |TY| ------------------------------------------------------------------------------- #. Hide the :guilabel:`OSM-WSM` layer in the :guilabel:`Layers` panel. #. Add the "ZAF CGS 1M Bedrock Lithostratigraphy" WMS server at this URL: ``http://196.33.85.22/cgi-bin/ZAF_CGS_Bedrock_Geology/wms`` #. Load the :guilabel:`BEDROCKGEOLOGY` layer into the map (you can also use the :menuselection:`Layer --> Add Layer -->` |addWmsLayer| :menuselection:`Add WMS/WMTS Layer...` button to open the Data Source Manager dialog). Remember to check that it's in the same :guilabel:`WGS 84 / World Mercator` projection as the rest of your map! #. You might want to set its :guilabel:`Encoding` to :guilabel:`JPEG` and its :guilabel:`Tile size` option to ``200`` by ``200``, so that it loads faster: .. figure:: img/bedrock_geology_layer.png :align: center .. admonition:: Answer :class: dropdown Your map should look like this (you may need to re-order the layers): .. figure:: img/geology_layer_result.png :align: center |moderate| |TY| ------------------------------------------------------------------------------- #. Hide all other WMS layers to prevent them from rendering unnecessarily in the background. #. Add the "OGC" WMS server at this URL: ``http://ogc.gbif.org:80/wms`` #. Add the :guilabel:`bluemarble` layer. .. admonition:: Answer :class: dropdown * Use the same approach as before to add the new server and the appropriate layer as hosted on that server: .. figure:: img/add_ogc_server.png :align: center .. figure:: img/add_bluemarble_layer.png :align: center * If you zoom into the |majorUrbanName| area, you'll notice that this dataset has a low resolution: .. figure:: img/low_resolution_dataset.png :align: center Therefore, it's better not to use this data for the current map. The Blue Marble data is more suitable at global or national scales |hard| |TY| ------------------------------------------------------------------------------- Part of the difficulty of using WMS is finding a good (free) server. * Find a new WMS at `directory.spatineo.com `_ (or elsewhere online). It must not have associated fees or restrictions, and must have coverage over the |majorUrbanName| study area. Remember that what you need in order to use a WMS is only its URL (and preferably some sort of description). .. admonition:: Answer :class: dropdown You may notice that many WMS servers are not always available. Sometimes this is temporary, sometimes it is permanent. An example of a WMS server that worked at the time of writing is the :guilabel:`World Mineral Deposits` WMS at http://apps1.gdr.nrcan.gc.ca/cgi-bin/worldmin_en-ca_ows. It does not require fees or have access constraints, and it is global. Therefore, it does satisfy the requirements. Keep in mind, however, that this is merely an example. There are many other WMS servers to choose from. |IC| ------------------------------------------------------------------------------- Using a WMS, you can add inactive maps as backdrops for your existing map data. |FR| ------------------------------------------------------------------------------- * `Spatineo Directory `_ * `OpenStreetMap.org list of WMS servers `_ |WN| ------------------------------------------------------------------------------- Now that you've added an inactive map as a backdrop, you'll be glad to know that it's also possible to add features (such as the other vector layers you added before). Adding features from remote servers is possible by using a Web Feature Service (WFS). That's the topic of the next lesson. .. Substitutions definitions - AVOID EDITING PAST THIS LINE This will be automatically updated by the find_set_subst.py script. If you need to create a new substitution manually, please add it also to the substitutions.txt file in the source folder. .. |FA| replace:: Follow Along: .. |FR| replace:: Further Reading .. |IC| replace:: In Conclusion .. |LS| replace:: Lesson: .. |TY| replace:: Try Yourself .. |WN| replace:: What's Next? .. |addWmsLayer| image:: /static/common/mActionAddWmsLayer.png :width: 1.5em .. |basic| image:: /static/common/basic.png .. |dataSourceManager| image:: /static/common/mActionDataSourceManager.png :width: 1.5em .. |hard| image:: /static/common/hard.png .. |majorUrbanName| replace:: Swellendam .. |moderate| image:: /static/common/moderate.png