The "Export for Bibliometric Mapping" option will export a .CSV file which is formatted to be used with the openly-available VOSviewer software programme from CWTS Leiden (http://www.vosviewer.com/download) or in the CiteSpace software (available here - external web page). These are software tools for constructing and visualizing bibliometric networks. These networks may for instance include journals, researchers, or individual publications, and they can be constructed based on citation, bibliographic coupling, co-citation, or co-authorship relations.
In order to use the exports in this way, simply download the VOSviewer tool from http://www.vosviewer.com/download, or CitSpace from here and create a bibliometric mapping export from Dimensions for importing into this. The export for bibliometric mapping is limited to a maximum number of 50,000 results, and is only available for publications data.