How to add a basemap

In this section the method for adding online basemaps to your map view will be explained.

1. After creating a new project or loading an existing one ensure some geo-referenced data are loaded into your map view, e.g. a 1D network or any GIS dataset added to the Layers panel.
   
2. The base mapping options are provided in a drop-down menu accessed from the Home tab of the main toolbar
   
3. Click on the Base Map button to access a menu of available mapping options
   
4. Click on an option to add it to your Map view as background mapping. Note that this will not add any new datasets to your Layers panel.
5. The base mapping requires a geo-projection to be defined for the map view. If your project currently does not have a geo-projection associated to it then you will be prompted to specify one. If you click Yes then a new window is displayed that lists all available projections and enables you to select one. Clicking OK assigns the selected projection to your project (and closes the geo-projection window).
   
   Your map should now display the selected mapping data as a background to your map view (always behind other layers). Note that this functionality requires an internet connection to work (and may make the map view respond slowly if the internet connection is slow).
   Note that you can review and edit your project projection setting by clicking on the Start tab of the main toolbar. The current projection setting is displayed on the Info page and a button is provided to access the projection selection window (as shown above).
6. Your selected projection should now be displayed on your Project Info page (accessed from the Start tab in main toolbar). Remember to save this setting by saving your project. Note however that the selected background mapping will not return automatically when you re-load the project in a later session. Flood Modeller’s default starting setting is to show no background mapping.

 Updating the background mapping

As you pan or zoom to different locations the background mapping will update automatically. Furthermore the level of detail shown will increase as you zoom in to a smaller area (and decrease as you zoom out).

You can change to a different background map source by selecting a different option from the Base Maps drop-down list. Note that you might need to change the map extents to trigger this update in the map view, e.g. pan a small distance.

Using the Base Maps projection 

Flood Modeller enables selected online base maps (Bing and Open Street Map) to be displayed in the map view, providing a useful back drop to model data. The base maps use the Pseudo-Mercator (WGS 84) map projection. Thus, if your project is set to a different projection, Flood Modeller will re-project the base map data onto the project projection. However, this conversion process can introduce an offset between adjacent base map tiles. In some locations the offset is sufficiently large to be visible. This can be seen in roads that traverse across multiple tiles. It can also be manifested by gaps appearing between tiles (shown by white squares), as shown below:

If you wish to avoid this effect, you can set the map view to use the base map projection, i.e. Pseudo-Mercator (WGS 84). This will ensure the base map tiles are perfectly aligned.