If you have a datasource which says which user is from which location then we will be able to do this.
USERNAME() can be used as a calculated field and we just need to do a join against your database to retrieve the location. You can have that as a filter on you dashboard. This way based on the user the dashboard is filtered to the user location.
Please let me know if this helps.
Could you be more specific ? Where is the location data stored ? If possible, please attach the sample workbook. It will be helpful.