The graphic layer Background map dynamically embeds maps and aerial images of map services into network display. The data matching the current network section is shown at the respective zoom level. You can optionally show the map data in shades of gray or pale colors, so as to not overpower the network display (User Manual: Dynamically embedding background maps provided on the Internet ).
Compared to static backgrounds, the display is controlled exclusively via graphic parameters and user preferences There are no additional functions for administration. The data is not saved to the system, so that this functionality requires a permanent Internet connection.
To use it, you need to select a coordinate system for the network. You can use any of the coordinate systems defined in Visum. The background maps are transformed to the coordinate system selected in Visum and are then displayed. If in Visum you select the coordinate system used by the map provider, no transformation is required and the background map can be displayed quicker. Most map services use a special type of Mercator projection (Coordinate systems). The projection files delivered with Visum include this coordinate system as so-called WGS 84 - Pseudo-Mercator (adapted EPSG 3857) (User Manual: Selecting a coordinate system). When you start a new session or open a new network, this coordinate system is your default setting. The definition of this coordinate system largely corresponds to the one defined in EPSG 3857, however, with minor changes that allow it to be used with common map services and Visum.
By default, Visum provides several map services in the Graphic parameters. You may also define map services that can be used alternatively (User Manual: Specifying default settings for inserting background maps).
To set up a user-defined map service, you need to know the URL structure and projection this service uses to call map sections. You then enter a URL template for the service. It contains several wildcards, e.g. for map section and zoom level parameters. When calling a specific map section, Visum replaces the wildcards with the current data (User Manual: Specifying default settings for inserting background maps). In the Graphic parameters and version file, map services are only referred to via their names. User-defined map services must have the same name on all computers using them. You can ensure this by exchanging a user preferences file (User Manual: Saving, opening and restoring user preferences). This makes sure that changes made to the configuration data of user-defined map services become effective in all the following Visum sessions, irrespective of the version file used.
