Every map projection is a distortion of the truth because it involves smashing an ellipsoid (the earth) onto a plane (the map). Map projections all have their respective pros and cons.
The quality of the map files provided from free services is generally not very good and the rendering speed can be unacceptably slow. If you need map images that are more responsive, then investigate for paid services. Tableau’s maps are created and maintained by San Francisco-based, Urban Mapping. Due to their familiarity with tableau software, Urban Mapping is a good place to start if you have special interactive map needs. Their maps confirm to Tile Map Service (TMS) that is used by Tableau. Urban Mapping provides free sample map files upon request. Their map files render more quickly than WMS services found on the Internet. Figure 5.16 compares a standard Tableau map with a custom map provided by Urban Mapping.
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Figure 5.16: Standard and custom maps
The map on the left is a standard Tableau map using the normal map style. The custom map on the right from Urban Mapping includes Chicago bus routes. The bus route map was enabled by copying a Tableau Map Source (tms) file supplied by Urban Mapping to C: Program File (x86) Tableau Tableau 8.0 Map sources. Map files that are placed into that map’s source directory appear as an option within Tableau’s map menu. To replace Tableau’s standard maps with any map service use the main menu and follow these steps:
By following these steps, the customized map will appear as an option under the map menu/ background maps. The name that appears for the custom map in the menu is whatever name you assign when establishing the connection to the map service. The steps required to share a WMS custom map with other Tableau users are:
Figure 5.17 displays a custom map image that came from a web mapping service at free of charge.
Figure 5.17: Custom (WMS) map
After entering the URL for the service, the connection name was edited to open Geo WMS server example. This name appears in figure 5.17 via the map menu. The satellite image layer was added to the view by selecting the “blue marble” map layer in the map layer menu. At the time of writing, open Geo WMS server was functional.
Using a web mapping service allows you to customize maps to fit your particular needs. In the next section, you’ll learn how to import custom image files to build map displays that meet your specific requirements.
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