I don't use maps that often, but I thought the maps and data were somewhat independent.
For example, if my data source is an Excel file with one row
If the State dimension is geographic > state, Tableau will create the lat/long and I can place these on the rows/columns shelf. Then I can zoom out to see all of the US.
I am using color coding for the sales per state,Some states have no data and I want to show them in a different color(not white or the background color.
A couple of possibilities that come to mind (though it will depend on your data source and structure as to what will work):
1. Create a list of all states as a flat file (or Excel). Connect to that and use it as the primary source of a data blend.
2. Use custom SQL to UNION some dummy rows of data that include all states with 0 as the value for the measure you want to use.
I'd be happy to take a look at some sample data or a packaged workbook!